79 results on '"General Chemistry"'
Search Results
2. Theoretical and experimental insight into zinc loading on mesoporous silica
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Maria Ziolek, Frederik Tielens, Tomasz Siodła, Izabela Sobczak, Faculty of Chemistry [Adam Mickiewicz], Adam Mickiewicz University in Poznań (UAM), Spectroscopie, Modélisation, Interfaces pour L'Environnement et la Santé (LCMCP-SMiLES), Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP), Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Departement of General Chemistry (ALGC) (ALG), Université libre de Bruxelles (ULB), National Science Centre in Poland (Grant No. 2013/10/E/ST5/00642), GENCI-[CCRT/CINES/IDRIS] (Grant 2016-[x2016082022]), CCRE of Université Pierre et Marie Curie, PL-Grid Infrastructure, and General Chemistry
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Materials science ,Chemistry(all) ,Silicon ,Inorganic chemistry ,Basicity ,chemistry.chemical_element ,02 engineering and technology ,Zinc ,010402 general chemistry ,DFT ,01 natural sciences ,Metal ,Molecular level ,Materials Science(all) ,X-ray photoelectron spectroscopy ,XPS ,General Materials Science ,Fourier transform infrared spectroscopy ,[CHIM.MATE]Chemical Sciences/Material chemistry ,General Chemistry ,Mesoporous silica ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Zn/MCF ,0104 chemical sciences ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Trigonal bipyramidal molecular geometry ,FTIR ,chemistry ,Chemical engineering ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology - Abstract
International audience; Zinc oxide species grafted on mesostructured cellular foam (MCF) silica are investigated using a combination of experimental and theoretical techniques. MCF is modelled using a realistic amorphous silica surface model surface slab. The most energetically favorable complexes grafted on the silica surface were identified and characterized at the molecular level. The Zn metal center was found in tetrahedral coordination. Moreover, the Si-O-Zn-OH species is found to be stabilized in a 5 fold coordinated silicon with an unusual trigonal bipyramidal geometry. A mechanism for the grafting process of the metal species on the support is proposed.
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- 2018
3. Photoactivation of titanium-oxo cluster [Ti6O6(OR)6(O2CtBu)6]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex
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Stephen E. Brown, Ioanna Mantaloufa, Ryan T. Andrews, Thomas J. Barnes, Martin R. Lees, Frank De Proft, Ana V. Cunha, Sebastian D. Pike, Faculty of Sciences and Bioengineering Sciences, Chemistry, and General Chemistry
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General Chemistry - Abstract
The molecular titanium-oxo cluster [Ti6O6(OiPr)6(O2CtBu)6] (1) can be photoactivated by UV light, resulting in a deeply coloured mixed valent (photoreduced) Ti (III/IV) cluster, alongside alcohol and ketone (photooxidised) organic products. Mechanistic studies indicate that a two-electron (not free-radical) mechanism occurs in this process, which utilises the cluster structure to facilitate multielectron reactions. The photoreduced products [Ti6O6(OiPr)4(O2CtBu)6(sol)2], sol = iPrOH (2) or pyridine (3), can be isolated in good yield and are structurally characterized, each with two, uniquely arranged, antiferromagnetically coupled d-electrons. 2 and 3 undergo onward oxidation under air, with 3 cleanly transforming into peroxide complex, [Ti6O6(OiPr)4(O2CtBu)6(py)(O2)] (5). 5 reacts with isopropanol to regenerate the initial cluster (1) completing a closed cycle, and suggesting opportunities for the deployment of these easily made and tuneable clusters for sustainable photocatalytic processes using air and light. The redox reactivity described here is only possible in a cluster with multiple Ti sites, which can perform multi-electron processes and can adjust its shape to accommodate changes in electron density.
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- 2023
4. Molecular Resolution Nanostructure and Dynamics of the Deep Eutectic Solvent—Graphite Interface as a Function of Potential
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Justin S. Freeman, Mesfin Haile Mamme, Jon Ustarroz, Gregory G. Warr, Hua Li, Rob Atkin, Materials and Chemistry, General Chemistry, and Electrochemical and Surface Engineering
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Biomaterials ,General Materials Science ,General Chemistry ,Biotechnology - Abstract
Interest in deep eutectic solvents (DESs), particularly for electrochemical applications, has boomed in the past decade because they are more versatile than conventional electrolyte solutions and are low cost, renewable, and non-toxic. The molecular scale lateral nanostructures as a function of potential at the solid–liquid interface—critical design parameters for the use of DESs as electrochemical solvents—are yet to be revealed. In this work, in situ amplitude modulated atomic force microscopy complemented by molecular dynamics simulations is used to probe the Stern and near-surface layers of the archetypal and by far most studied DES, 1:2 choline chloride:urea (reline), at the highly orientated pyrolytic graphite surface as a function of potential, to reveal highly ordered lateral nanostructures with unprecedented molecular resolution. This detail allows identification of choline, chloride, and urea in the Stern layer on graphite, and in some cases their orientations. Images obtained after the potential isswitched from negative to positive show the dynamics of the Stern layer response, revealing that several minutes are required to reach equilibrium. These results provide valuable insight into the nanostructure and dynamics of DESs at the solid–liquid interface, with implications for the rational design of DESs for interfacial applications.
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- 2023
5. SuFEx-enabled, chemoselective synthesis of triflates, triflamides and triflimidates
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Steven Verhelst, Fien Hoppenbrouwers, Mercedes Alonso, Wim De Borggraeve, Lauren Voets, Joachim Demaerel, Ruben Van Lommel, Bing-Yu Li, Faculty of Sciences and Bioengineering Sciences, Chemistry, and General Chemistry
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Chemistry ,Science & Technology ,Chemistry, Multidisciplinary ,Physical Sciences ,General Chemistry - Abstract
Sulfur(VI) Fluoride Exchange (SuFEx) chemistry has emerged as a next-generation click reaction, designed to assemble functional molecules quickly and modularly. Here, we report the ex situ generation of trifluoromethanesulfonyl fluoride (CF3SO2F) gas in a two chamber system, and its use as a new SuFEx handle to efficiently synthesize triflates and triflamides. This broadly tolerated protocol lends itself to peptide modification or to telescoping into coupling reactions. Moreover, redesigning the SVI–F connector with a S=O → S=NR replacement, furnished the analogous triflimidoyl fluorides as SuFEx electrophiles, which were engaged in the synthesis of rarely reported triflimidate esters. Notably, experiments showed H2O to be the key towards achieving chemoselective trifluoromethanesulfonation of phenols vs. amine groups, a phenomenon best explained—using ab initio metadynamics simulations—by a hydrogen bonded termolecular transition state for the CF3SO2F triflylation of amines. Sulfur(VI) Fluoride Exchange (SuFEx) chemistry has emerged as a next-generation click reaction, designed to assemble functional molecules quickly and modularly. Here, we report the ex situ generation of trifluoromethanesulfonyl fluoride (CF3SO2F) gas in a two chamber system, and its use as a new SuFEx handle to efficiently synthesize triflates and triflamides. This broadly tolerated protocol lends itself to peptide modification or to telescoping into coupling reactions. Moreover, redesigning the SVI–F connector with a S=O → S=NR replacement, furnished the analogous triflimidoyl fluorides as SuFEx electrophiles, which were engaged in the synthesis of rarely reported triflimidate esters. Notably, experiments showed H2O to be the key towards achieving chemoselective trifluoromethanesulfonation of phenols vs. amine groups, a phenomenon best explained—using ab initio metadynamics simulations—by a hydrogen bonded termolecular transition state for the CF3SO2F triflylation of amines. ispartof: Chemical Science vol:13 issue:8 pages:1-10 ispartof: location:England status: published
- Published
- 2022
6. Modulation of Metal Carbonyl Stretching Frequencies in the Second Coordination Sphere through the Internal Stark Effect
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Gemma L. Parker, Ruben Van Lommel, Nil Roig, Mercedes Alonso, Adrian B. Chaplin, Chemistry, and General Chemistry
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DYNAMICS ,Science & Technology ,bond theory ,Chemistry, Multidisciplinary ,Organic Chemistry ,NICKEL ,Molecular Conformation ,General Chemistry ,RHODIUM ,Ligands ,electrostatic interactions ,Ruthenium ,Catalysis ,REACTIVITY ,IRIDIUM COMPLEXES ,MACROCYCLIC PNP ,ELECTRONIC-PROPERTIES ,Chemistry ,rotaxanes ,carbonyl ligands ,Physical Sciences ,Rhodium ,LIGANDS ,macrocyclic ligands ,BASIS-SETS - Abstract
Spectroscopic and computational examination of a homologous series of rhodium(I) pybox carbonyl complexes has revealed a correlation between the conformation of the flanking aryl-substituted oxazoline donors and the carbonyl stretching frequency. This relationship is also observed experimentally for octahedral rhodium(III) and ruthenium(II) variants and cannot be explained through the classical, Dewar-Chatt-Duncanson, interpretation of metal-carbonyl bonding. Instead, these findings are reconciled by local changes in the magnitude of the electric field that is projected along the metal-carbonyl vector: the internal Stark effect. ispartof: CHEMISTRY-A EUROPEAN JOURNAL vol:28 issue:69 ispartof: location:Germany status: published
- Published
- 2022
7. Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins
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Irene Casademont‐Reig, Tatiana Woller, Victor García, Julia Contreras‐García, William Tiznado, Miquel Torrent‐Sucarrat, Eduard Matito, Mercedes Alonso, European Commission, Chemistry, and General Chemistry
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charged macrocycles ,annulene model ,Organic Chemistry ,porphyrinoids ,aromaticity ,General Chemistry ,ring currents ,Catalysis - Abstract
Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins. M.A. and I.C.R. wish to acknowledge the VUB for a Strategic Research Program awarded to ALGC. The resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by the Research Foundation - Flanders (FWO), and the Flemish Government. I.C.R. acknowledges co-funding from the European Union′s Horizon 2020 research and innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. It has been also supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), Gobierno Vasco (IT1346-19, IT1254-19, and PIBA19-0004), and the DIPC (DIPC_INV_003132). Open Access funding provided by University of Basque Country.
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- 2022
8. Reactivity of a N‐Coordinated Germylene‐Borane Complex: From Ge→B to Ge→Ga Coordination
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Dominik Vítek, Aleš Růžička, Lise Vermeersch, Libor Dostál, Jan Turek, Roman Jambor, Chemistry, Faculty of Sciences and Bioengineering Sciences, and General Chemistry
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germylene ,NMR spectroscopy ,Organic Chemistry ,proton affinity ,group 13 metals ,General Chemistry ,coordination bond ,Catalysis - Abstract
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 (1; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 (2) and [LGe⋅BH3]2 (3) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 (4) and L(Cl)Ge⋅GaCl3 (5) without a GeII→B interaction. In 5, an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1−5. The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.
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- 2022
9. Non-fluorinated non-solvating cosolvent enabling superior performance of lithium metal negative electrode battery
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Junyeob Moon, Dong Ok Kim, Lieven Bekaert, Munsoo Song, Jinkyu Chung, Danwon Lee, Annick Hubin, Jongwoo Lim, Materials and Chemistry, Faculty of Engineering, General Chemistry, Earth System Sciences, and Electrochemical and Surface Engineering
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Multidisciplinary ,General Physics and Astronomy ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology - Abstract
The growth of dendrites on lithium metal electrodes is problematic because it causes irreversible capacity loss and safety hazards. Localised high-concentration electrolytes (LHCEs) can form a mechanically stable solid-electrolyte interphase and prevent uneven growth of lithium metal. However, the optimal physicochemical properties of LHCEs have not been clearly determined which limits the choice to fluorinated non-solvating cosolvents (FNSCs). Also, FNSCs in LHCEs raise environmental concerns, are costly, and may cause low cathodic stability owing to their low lowest unoccupied molecular orbital level, leading to unsatisfactory cycle life. Here, we spectroscopically measured the Li+ solvation ability and miscibility of candidate non-fluorinated non-solvating cosolvents (NFNSCs) and identified the suitable physicochemical properties for non-solvating cosolvents. Using our design principle, we proposed NFNSCs that deliver a coulombic efficiency up to 99.0% over 1400 cycles. NMR spectra revealed that the designed NFNSCs were highly stable in electrolytes during extended cycles. In addition, solvation structure analysis by Raman spectroscopy and theoretical calculation of Li+ binding energy suggested that the low ability of these NFNSCs to solvate Li+ originates from the aromatic ring that allows delocalisation of electron pairs on the oxygen atom.
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- 2022
10. Conceptual density functional theory under pressure
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J. Eeckhoudt, T. Bettens, P. Geerlings, R. Cammi, B. Chen, M. Alonso, F. De Proft, Chemistry, Faculty of Sciences and Bioengineering Sciences, General Chemistry, and Vriendenkring VUB
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General Chemistry - Abstract
High pressure chemistry offers the chemical community a range of possibilities to control chemical reactivity, develop new materials and fine-tune chemical properties. Despite the large changes that extreme pressure brings to the table, the field has mainly been restricted to the effects of volume changes and thermodynamics with less attention devoted to electronic effects at the molecular scale. This paper combines the conceptual DFT framework for analyzing chemical reactivity with the XP-PCM method for simulating pressures in the GPa range. Starting from the new derivatives of the energy with respect to external pressure, an electronic atomic volume and an atomic compressibility are found, comparable to their enthalpy analogues, respectively. The corresponding radii correlate well with major known sets of this quantity. The ionization potential and electron affinity are both found to decrease with pressure using two different methods. For the electronegativity and chemical hardness, a decreasing and increasing trend is obtained, respectively, and an electronic volume-based argument is proposed to rationalize the observed periodic trends. The cube of the softness is found to correlate well with the polarizability, both decreasing under pressure, while the interpretation of the electrophilicity becomes ambiguous at extreme pressures. Regarding the electron density, the radial distribution function shows a clear concentration of the electron density towards the inner region of the atom and periodic trends can be found in the density using the Carbó quantum similarity index and the Kullback-Leibler information deficiency. Overall, the extension of the CDFT framework with pressure yields clear periodic patterns.
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- 2022
11. Elucidation of the IR of Cu and Mn substituted intraframework SiBEA zeolites
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Etienne P. Hessou, Michael Badawi, Laetitia Valentin, Guy Atohoun, Stanislaw Dzwigaj, Monica Calatayud, Frederik Tielens, Chemistry, and General Chemistry
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CuSiBEA ,Chemistry(all) ,IR ,MnSiBEA ,zeolites ,General Chemistry ,DFT ,Catalysis - Abstract
Copper and manganese modified zeolites play key roles in selective oxidation catalytic reactions. Combining Density Functional Perturbation Theory (DFPT) implemented in VASP, and infrared spectroscopy experiments, we have studied and elucidated the incorporation of Cu2+ and Mn2+ in the framework of SiBEA zeolite. Six isomers are investigated for both models CuSiBEA and MnSiBEA. The energy stability study identified the most stable isomer in each case, which correspond to M-O2 bent moieties in the vicinity of hydroxyl groups. The isomers are then characterized by experimental and theoretical IR spectra. Both experimental and calculated IR spectra are in good agreement highlighting the presence of active sites (Cu-OH and Mn-OH) in the obtained models. The accurate molecular description of the nature of the active sites presented in this work will be important for understanding the catalysis going on and for developing novel catalytic processes.
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- 2022
12. Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation
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Frederik Tielens, Stefaan Cottenier, Mercedes Alonso, Bert M. Weckhuysen, Paul W. Ayers, Frank De Proft, Xavier Deraet, Jan Turek, General Chemistry, Chemistry, and Faculty of Sciences and Bioengineering Sciences
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010405 organic chemistry ,Chemistry ,Organic Chemistry ,Fermi level ,General Chemistry ,010402 general chemistry ,01 natural sciences ,London dispersion force ,Catalysis ,0104 chemical sciences ,symbols.namesake ,Chemical physics ,Atom ,symbols ,Density of states ,Oxophilicity ,Reactivity (chemistry) ,Density functional theory ,van der Waals force - Abstract
The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8–10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from −1.40 to −1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between −2.20 and −2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.
- Published
- 2021
13. Investigation of electronic and photocatalytic properties of AgTi2(PO4)3 NASICON-type phosphate: Combining experimental data and DFT calculations
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Ali Moussadik, Nour-eddine Lazar, Driss Mazkad, Flavio Siro Brigiano, Kitty Baert, Tom Hauffman, Abdellah Benzaouak, Younes Abrouki, Mohamed Kacimi, Frederik Tielens, Mohammed Halim, Adnane El Hamidi, Faculty of Sciences and Bioengineering Sciences, Chemistry, General Chemistry, Electrochemical and Surface Engineering, Materials and Chemistry, and Materials Characterisation
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General Chemical Engineering ,General Physics and Astronomy ,General Chemistry - Abstract
Ag-based semiconductors have attracted significant attention as promising visible-light photocatalysts for environmental purification. In this study, electronic and photocatalytic properties of AgTi2(PO4)3 NASICON-type phosphate, have been addressed in detail, combining experimental results and theoretical calculations. The as-prepared sample was characterized for its morphological, structural and optical properties by various techniques. The generalized gradient approximation by Perdew-Burke-Ernzerhof (GGA-PPE) within density functional theory (DFT) was used to investigate the electronic structure. We have applied corrective Hubbard U terms to Ti 3d orbitals in order to better reproduce the experimental band gap of 2.6 eV. The photocatalytic activity has then been performed for rhodamine B dye degradation under visible light illumination. Efficient dye degradation up to 97.2% was achieved in 120 min. In addition, the catalyst exhibited good stability over four consecutive cycles. Finally, combining experimental and theoretical findings, the origin of the photocatalytic activity was identified and a photodegradation mechanism was proposed.
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- 2023
14. Nanostructured materials and heterogeneous catalysis : a succinct review regarding DeNox catalysis
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Dominique Bazin, Jelle Vekeman, Qing Wang, Xavier Deraet, Frank De Proft, Hazar Guesmi, Frederik Tielens, Chemistry, Faculty of Sciences and Bioengineering Sciences, and General Chemistry
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NO adsorption ,NANOMETER-SCALE ,General Chemical Engineering ,SURFACES ,IN-SITU ,DeNox catalysis ,DFT approach ,NOBLE-METAL ,Building and Construction ,General Chemistry ,CLOSE-PACKED TRANSITION ,Metallic cluster ,DENSITY-FUNCTIONAL THEORY ,SYNCHROTRON-RADIATION ,Chemistry ,Nanoscience ,BIMETALLIC CATALYSTS ,RH(111) SURFACE ,X-RAY ,Electrical and Electronic Engineering - Abstract
In this contribution, we would like to underline the peculiar chemical properties of nanome-ter scale metallic particles. To attain this goal, we select the case of DeNox catalysis (NOx reduction to nitrogen molecule) for which such nanomaterials play a crucial role. Experimental data as well as re-cent theoretical calculation through density functional theory are used to assess the relationship be-tween the adsorption mode of NO and the behaviour of nanometre scale metallic particles. Resume. Les oxydes d'azote NOx issus des gaz d'echappement des moteurs Diesel participent a la de-terioration de l'environnement, la moitie des emissions de NO leur etant imputable. Le monoxyde d'azote provient essentiellement des reactions chimiques entre l'azote de l'air et l'oxygene qui s'eta-blissent a tres haute temperature. Le defi consiste a reduire cette emission qui doit etre selective en azote (eviter la formation de N2O ou de NO2). En ce qui concerne les catalyseurs mis en & OELIG;uvre, on en distingue trois groupes : les oxydes de metaux, les metaux nobles et les zeolites. A partir de donnees ex-perimentales obtenues sur l'adsorption du NO sur des agregats monometalliques, une relation entre les modes d'adsorption de cette molzcule (adsorption molzculaire/chimisorption) et la rzponse de l'agrzgat mztallique face a cette adsorption (croissance/dissociation) a ztz proposze. Les ztudes thzo-riques baszes sur la thzorie de la fonctionnelle de la densitz confortent cette relation. Cette contri-bution przsente l'ensemble de ces rzsultats expzrimentaux et thzoriques et tache de montrer l'aspect przdictif d'une telle relation.
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- 2022
15. Extending conceptual DFT to include external variables: the influence of magnetic fields
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Robin Francotte, Tom J. P. Irons, Andrew M. Teale, Frank de Proft, Paul Geerlings, Vriendenkring VUB, Chemistry, General Chemistry, and Faculty of Sciences and Bioengineering Sciences
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General Chemistry - Abstract
An extension of conceptual DFT to include the influence of an external magnetic field is proposed in the context of a program set up to cope with the ever increasing variability of reaction conditions and concomitant reactivity. The two simplest global reactivity descriptors, the electronic chemical potential (μ) and the hardness (η), are considered for the main group atoms H-Kr using current density-functional theory. The magnetic field strength, |B|, is varied between 0.0 and 1.0 B0 = ħe−1a0−2 ≈ 2.3505 × 105 T, encompassing the Coulomb and intermediate regimes. The carbon atom is studied as an exemplar system to gain insight into the behaviour of the neutral, cationic and anionic species under these conditions. Their electronic configurations change with increasing |B|, leading to a piecewise behaviour of the ionization energy (I) and electron affinity (A) values as a function of |B|. This results in complex behaviour of properties such as the electronegativity χ = −1/2(I + A) = −μ and hardness η = 1/2(I − A). This raises an interesting question: to what extent are atomic properties periodic in the presence of a magnetic field? In the Coulomb regime, close to |B| = 0, we find the familiar periodicity of the atomic properties, and make the connections to response functions central to conceptual DFT. However, as the field increases in the intermediate regime configurational changes of the atomic species lead to discontinuous changes in their properties; fundamentally changing their behaviour, which is illustrated by constructing a periodic table of χ and η values at |B| = 0.5 B0. These values tend to increase for groups 1-2 and decrease for groups 16-18, leading to a narrower range overall and suggesting substantial changes in the chemistry of the main group elements. Changes within each group are also examined as a function of |B|. These are more complex to interpret due to the larger number of configurations accessible to heavier elements at high field. This is illustrated for group 17 where Cl and Br have qualitatively different configurations to their lighter cogener at |B| = 0.5 B0. The insight into periodic trends in strong magnetic fields may provide a crucial starting point for predicting chemical reactivity under these exotic conditions.
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- 2022
16. How Do Local Reactivity Descriptors Shape the Potential Energy Surface Associated with Chemical Reactions? The Valence Bond Delocalization Perspective
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Sason Shaik, Frank De Proft, Paul Geerlings, Thijs Stuyver, Chemistry, Vriendenkring VUB, Quantum Chemistry - Molecular Modelling, and General Chemistry
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Chemistry ,Perspective (graphical) ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Chemical reaction ,Catalysis ,Article ,Addition/Correction ,0104 chemical sciences ,Delocalized electron ,Colloid and Surface Chemistry ,Chemical physics ,Potential energy surface ,Valence bond theory ,Density functional theory ,Reactivity (chemistry) ,Fukui function - Abstract
How do local reactivity descriptors, such as the Fukui function and the local spin density distribution, shape the potential energy surface (PES) associated with chemical reactions and thus govern reactivity trends and regioselective preferences? This is the question that is addressed here through a qualitative valence bond (VB) analysis. We demonstrate that common density functional theory (DFT)-based local reactivity descriptors can essentially be regarded-in one way or another-as indirect measures of delocalization, i.e., resonance stabilization, of the reactants within VB theory. The inherent connection between (spatial) delocalization and (energetic) resonance stabilization embedded in VB theory provides a natural and elegant framework for analyzing and comprehending the impact of individual local reactivity descriptors on the global PES. Our analysis provides new insights into the role played by local reactivity descriptors and illustrates under which conditions they can sometimes fail to predict reactivity trends and regioselective preferences, e.g., in the case of ambident reactivity. This treatment constitutes a first step toward a unification of VB theory and conceptual DFT.
- Published
- 2020
17. The hunt for reactive alkynes in bio-orthogonal click reactions: insights from mechanochemical and conceptual DFT calculations†
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Frank De Proft, Paul Geerlings, Mercedes Alonso, Tom Bettens, Chemistry, Faculty of Sciences and Bioengineering Sciences, Vriendenkring VUB, Quantum Chemistry - Molecular Modelling, and General Chemistry
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Chemistry ,Materials science ,Nucleophile ,Chemical physics ,Bent molecular geometry ,Molecule ,Density functional theory ,Linear molecular geometry ,Reactivity (chemistry) ,Context (language use) ,General Chemistry ,Physics::Chemical Physics ,Triple bond - Abstract
In our effort to implement the mechanical force used to activate single molecules in mechanochemistry in the context of conceptual density functional theory, we present a theoretical investigation of strained alkynes for rationalizing structural trends as well as the reactivity of cyclic alkynes that are of great importance in in vivo click reactions. The strain on the triple bond in cyclic alkynes is modeled by angular constraints in a 2-butyne fragment and the corresponding bending force is calculated by means of an extended COGEF (constrained geometries simulate external forces) model. In general, the force required to bend the triple bond is smaller with electron-withdrawing groups on the propargylic C-atom, which elegantly results in smaller angles around the triple bond in cyclic alkynes with such substitution pattern. By means of conceptual DFT descriptors, the electrophilic and nucleophilic character of bent triple bonds was investigated revealing moderate activation for small distortions from the linear geometry (0° to 15°) and a drastically more reactive π-space if the triple bond is bent further. This analysis of the intrinsic reactivity of the triple bond is in line with experimental observations, explaining the reactive nature of cyclooctynes and cycloheptynes, whereas larger cyclic systems do not drastically activate the triple bond., The force required to bend alkynes increases linearly with the angle and depends on the substituent pattern. The reactivity of the triple bond does not readily increase and is less influenced by the substituent pattern for larger bends.
- Published
- 2019
18. Sn,P-coordinated Ru cation: a robust catalyst for aerobic oxidations of benzylamine and benzyl alcohol
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Jens Beckmann, Jan Turek, Jiří Tydlitát, Aleš Růžička, Roman Jambor, Libor Dostál, Michal Aman, Chemistry, and General Chemistry
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Ligand ,Reducing agent ,Metals and Alloys ,Ionic bonding ,General Chemistry ,Medicinal chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Benzylamine ,chemistry ,Benzyl alcohol ,Materials Chemistry ,Ceramics and Composites ,Naphthalene - Abstract
A stable ionic κ2Sn,P-coordinated Ru complex shows excellent catalytic activity in aerobic oxidations of benzylamine and benzyl alcohol. This complex is stabilized by a stannylene-phosphine peri-substituted naphthalene ligand, which can act as either a reducing agent for a Ru(III) complex or as a κ2Sn,P-chelating ligand for Ru(II) compounds.
- Published
- 2021
19. Fine-Tuning of Nonlinear Optical Contrasts of Hexaphyrin-Based Molecular Switches Using Inverse Design
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Eline Desmedt, Tatiana Woller, Jos L. Teunissen, Freija De Vleeschouwer, Mercedes Alonso, Chemistry, Faculty of Sciences and Bioengineering Sciences, and General Chemistry
- Subjects
Chemistry ,expanded porphyrins ,best-first search algorithm ,nonlinear optical properties ,(time-dependent) density functional theory ,General Chemistry ,inverse design ,molecular switches ,QD1-999 ,Original Research - Abstract
In the search for new nonlinear optical (NLO) switching devices, expanded porphyrins have emerged as ideal candidates thanks to their tunable chemical and photophysical properties. Introducing meso-substituents to these macrocycles is a successful strategy to enhance the NLO contrasts. Despite its potential, the influence of meso-substitution on their structural and geometrical properties has been scarcely investigated. In this work, we pursue to grasp the underlying pivotal concepts for the fine-tuning of the NLO contrasts of hexaphyrin-based molecular switches, with a particular focus on the first hyperpolarizability related to the hyper-Rayleigh scattering (βHRS). Building further on these concepts, we also aim to develop a rational design protocol. Starting from the (un)substituted hexaphyrins with various π-conjugation topologies and redox states, structure-property relationships are established linking aromaticity, photophysical properties and βHRS responses. Ultimately, inverse molecular design using the best-first search algorithm is applied on the most favorable switches with the aim to further explore the combinatorial chemical compound space of meso-substituted hexaphyrins in search of high-contrast NLO switches. Two definitions of the figure-of-merit of the switch performance were used as target objectives in the optimization problem. Several meso-substitution patterns and their underlying characteristics are identified, uncovering molecular symmetry and the electronic nature of the substituents as the key players for fine-tuning the βHRS values and NLO contrasts of hexaphyrin-based switches.
- Published
- 2021
20. Trapping of Ag+, Cu2+, and Co2+ by faujasite zeolite Y
- Author
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Michael Badawi, Adrian Bonilla-Petriciolet, Frederik Tielens, Guilherme Luiz Dotto, Matias Schadeck Netto, Etienne Paul Hessou, Lotfi Sellaoui, Jerosha Ifthikar, Luis F.O. Silva, Zhuqi Chen, Chemistry, and General Chemistry
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Materials science ,Ion exchange ,Cationic exchange ,Chemistry(all) ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Faujasite ,engineering.material ,Endothermic process ,Industrial and Manufacturing Engineering ,Ion ,DFT simulation ,Adsorption ,chemistry ,Faujasite-type zeolite Y ,engineering ,Chemical Engineering(all) ,Environmental Chemistry ,Density functional theory ,Physical modelling ,Zeolite ,Cobalt - Abstract
This work evaluated the potential of a synthesized faujasite-type zeolite Y as an adsorbent for the removal of relevant heavy metals such as silver (Ag+), copper (Cu2+), and cobalt (Co2+). The adsorption data of Ag+, Cu2+, and Co2+ ions were determined experimentally at pH 6 and temperatures of 298, 308, and 318 K. Two theoretical approaches have been applied based on statistical physics modeling and density functional theory (DFT) to understand and characterize the ion exchanges involved in the removal of all metals. Results showed that this zeolite was more efficient for the adsorption of Ag+ via cation-exchange. Based on the physical modelling, the removal of heavy metals on this zeolite was mono and multi-ionic (simple and multi-interactions), where the ions interacted via one and two adsorption sites. It was also noted that the temperature increment generated more available functional groups of the zeolite, facilitating the access to the smaller cavities and the interactions with the adsorbent. Adsorption energies for removing these metals with tested zeolite were slightly endothermic and were consistent with the typical values reported for ion exchange systems of heavy metals + zeolites. DFT results demonstrated that these cationic exchange energies depend on the nature of precursor salt, but with the same ranking. Both statistical and DFT approaches agreed that exchange Ag+ in zeolite Y was easier than Cu2+ and Co2+. Overall, the application of both theoretical approaches provided a reliable interpretation of the adsorption mechanism.
- Published
- 2021
21. TITAN: A Code for Modeling and Generating Electric Fields—Features and Applications to Enzymatic Reactivity
- Author
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Jing Huang, David Danovich, Sason Shaik, Thijs Stuyver, Dibyendu Mallick, Faculty of Sciences and Bioengineering Sciences, Chemistry, and General Chemistry
- Subjects
Physics ,010304 chemical physics ,Hydrogen transfer ,General Chemistry ,Molecular Dynamics Simulation ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Computational Mathematics ,symbols.namesake ,Molecular dynamics ,Matrix (mathematics) ,Cytochrome P-450 Enzyme System ,Electricity ,Chemical physics ,Electric field ,0103 physical sciences ,symbols ,Code (cryptography) ,Coulomb ,Quantum Theory ,Reactivity (chemistry) ,Titan (rocket family) ,Software - Abstract
We present here a versatile computational code named "elecTric fIeld generaTion And maNipulation (TITAN)," capable of generating various types of external electric fields, as well as quantifying the local (or intrinsic) electric fields present in proteins and other biological systems according to Coulomb's Law. The generated electric fields can be coupled with quantum mechanics (QM), molecular mechanics (MM), QM/MM, and molecular dynamics calculations in most available software packages. The capabilities of the TITAN code are illustrated throughout the text with the help of examples. We end by presenting an application, in which the effects of the local electric field on the hydrogen transfer reaction in cytochrome P450 OleTJE enzyme and the modifications induced by the application of an oriented external electric field are examined. We find that the protein matrix in P450 OleTJE acts as a moderate catalyst and that orienting an external electric field along the Fe─O bond of compound I has the biggest impact on the reaction barrier. The induced catalysis/inhibition correlates with the calculated spin density on the O-atom. © 2019 Wiley Periodicals, Inc.
- Published
- 2019
22. Diradical Character as a Guiding Principle for the Insightful Design of Molecular Nanowires with an Increasing Conductance with Length
- Author
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Yuta Tsuji, Frank De Proft, Tao Zeng, Thijs Stuyver, Paul Geerlings, Faculty of Economic and Social Sciences and Solvay Business School, Department of Bio-engineering Sciences, Faculty of Sciences and Bioengineering Sciences, Vriendenkring VUB, Quantum Chemistry - Molecular Modelling, Chemistry, and General Chemistry
- Subjects
molecular wires ,Chemistry(all) ,negative attenuation factor ,Nanowire ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Molecular wire ,Materials Science(all) ,General Materials Science ,single molecule electronics ,Physics ,Condensed matter physics ,Diradical ,Mechanical Engineering ,Conductance ,Molecular scale electronics ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,diradical character ,0104 chemical sciences ,Character (mathematics) ,0210 nano-technology - Abstract
In recent years, a considerable interest has grown in the design of molecular nanowires with an increasing conductance with length. The development of such nanowires is highly desirable because they could play an important role in future molecular-scale circuitry. Whereas the first experimental observation of this nonclassical behavior still has to be realized, a growing number of candidate wires have been proposed theoretically. In this Letter, we point out that all the wires with an anti-Ohmic increasing conductance with length proposed so far share a common characteristic: their diradical character increases with length. The conceptual connection between diradical character and conductance enables a systematic design of such anti-Ohmic wires and explains the difficulty in their syntheses. A strategy is proposed to balance the stability and conductance so that this nonclassical phenomenon can be observed.
- Published
- 2018
23. Mechanochemically Triggered Topology Changes in Expanded Porphyrins
- Author
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Frank De Proft, Andreas Dreuw, Marvin Hoffmann, Paul Geerlings, Mercedes Alonso, Tom Bettens, Chemistry, Faculty of Sciences and Bioengineering Sciences, Vriendenkring VUB, Quantum Chemistry - Molecular Modelling, and General Chemistry
- Subjects
Molecular switch ,topology ,Full Paper ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,General Chemistry ,Full Papers ,010402 general chemistry ,Topology ,Mechanical force ,Network topology ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Molecular switches ,Mechanochemistry ,Expanded porphyrins ,Molecule ,Quantum ,JEDI analysis ,Mechanical energy - Abstract
A hitherto unexplored class of molecules for molecular force probe applications are expanded porphyrins. This work proves that mechanical force is an effective stimulus to trigger the interconversion between Hückel and Möbius topologies in [28]hexaphyrin, making these expanded porphyrins suitable to act as conformational mechanophores operating at mild (sub‐1 nn) force conditions. A straightforward approach based on distance matrices is proposed for the selection of pulling scenarios that promote either the planar Hückel topology or the three lowest lying Möbius topologies. This approach is supported by quantum mechanochemical calculations. Force distribution analyses reveal that [28]hexaphyrin selectively allocates the external mechanical energy to molecular regions that trigger Hückel–Möbius interconversions, explaining why certain pulling scenarios favor the Hückel two‐sided topology and others favor Möbius single‐sided topologies. The meso‐substitution pattern on [28]hexaphyrin determines whether the energy difference between the different topologies can be overcome by mechanical activation., Use the force: The Hückel and Möbius topology of [28]hexaphyrin can be mechanically locked by applying an external pulling force to different meso positions in a sub‐nano‐Newton force regime. The mechanical energy is distributed to a specific region in the molecule to trigger the interconversion.
- Published
- 2021
24. Mapping surface segregation of single-atom Pt dispersed in M surfaces (M = Cu, Ag, Au, Ni, Pd, Co, Rh and Ir) under hydrogen pressure at various temperatures
- Author
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Frederik Tielens, Beien Zhu, Hazar Guesmi, Didier Tichit, Qing Wang, Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier (ICGM ICMMM), Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Université Montpellier 1 (UM1)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut de Chimie du CNRS (INC), Institute of Applied Physics [Shanghai], Chinese Academy of Sciences [Beijing] (CAS), Vrije Universiteit Brussel (VUB), Chemistry, and General Chemistry
- Subjects
Materials science ,Hydrogen ,Chemistry(all) ,General Physics and Astronomy ,Nanoparticle ,chemistry.chemical_element ,02 engineering and technology ,Physics and Astronomy(all) ,010402 general chemistry ,01 natural sciences ,DFT ,Structure stability ,Catalysis ,Metal ,Atom ,Reactivity (chemistry) ,Bimetallic strip ,Single Atom alloys ,Nano alloys ,General Chemistry ,Surfaces and Interfaces ,[CHIM.CATA]Chemical Sciences/Catalysis ,[CHIM.MATE]Chemical Sciences/Material chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,chemistry ,visual_art ,visual_art.visual_art_medium ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Physical chemistry ,Density functional theory ,0210 nano-technology - Abstract
International audience; Single-atom alloys (SAAs) are emerging materials containing isolated metal atoms dispersed on host metal surfaces, exhibiting unique reactivity compared with the corresponding monometallic counterparts. However, the stability of the isolated atoms in the host metal has hardly been studied, although, metal segregation has been commonly observed in bimetallic nanoparticles under reaction conditions. In this work we focus on single-atom Pt anchored on various metallic support surfaces. Density Functional Theory (DFT) calculations coupled with environmental segregation energy analysis are performed to map the segregation trends of 22 different Pt-SAA surfaces under various hydrogen conditions. The results show the high stability of single-atom Pt in Ni, Co, Rh and Ir host metallic surfaces while no stability is predicted on Au and Ag surfaces. For Pd and Cu host supports, the single-atom Pt is found to be stable on specific surface facets and within definite temperature and pressure conditions. This work brings an important understanding of SAA systems through the prediction of of surface atomic ordering changes under operating conditions which related to the reactivity will ultimately allow the design of more efficient catalysts.
- Published
- 2021
25. Morphology of Calcium Oxalate Polyhydrates: A Quantum Chemical and Computational Study
- Author
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Théau Debroise, Thomas Sedzik, Christian Bonhomme, Frederik Tielens, Yangyang Su, Jelle Vekeman, Spectroscopie, Modélisation, Interfaces pour L'Environnement et la Santé (LCMCP-SMiLES), Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP), Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Materials Modeling Group [Brussel], General Chemistry [Brussel] (ALGC), Vrije Universiteit Brussel [Bruxelles] (VUB)-Vrije Universiteit Brussel [Bruxelles] (VUB), and Chemistry
- Subjects
Morphology (linguistics) ,010405 organic chemistry ,Relaxation (NMR) ,Calcium oxalate ,Solvation ,chemistry.chemical_element ,Crystal growth ,General Chemistry ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Calcium ,010402 general chemistry ,Condensed Matter Physics ,01 natural sciences ,Surface energy ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,[CHIM]Chemical Sciences ,General Materials Science ,Density functional theory - Abstract
International audience; Monohydrated and dihydrated calcium oxalates have been widely studied in the literature because of their role in urolithiasis, a mammal pathology responsible for the formation of stones in the kidney. It is clear that the physicochemical environment plays a crucial role in the crystal growth and the resulting morphologies of calcium oxalates. To study these processes, reliable models for the calcium oxalates’ faces, exposed to water and potential additives, are needed. Here, we have used a total surface energy minimization approach to predict the crystal morphology of the calcium oxalate monohydrate and dihydrate phases. Surface energies were calculated at density functional theory level, taking into account surface relaxation and the effect of solvation. An excellent agreement was found between theoretically predicted morphologies and their experimental counterparts obtained by SEM, clearly demonstrating the importance of the inclusion of water in the model for the prediction of morphologies.
- Published
- 2020
26. Solvent Organization and Rate Regulation of a Menshutkin Reaction by Oriented External Electric Fields are Revealed by Combined MD and QM/MM Calculations
- Author
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Thijs Stuyver, Surajit Kalita, Sason Shaik, Kshatresh Dutta Dubey, Chemistry, and General Chemistry
- Subjects
Chemistry ,Rate regulation ,Menshutkin reaction ,Thermodynamics ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Article ,0104 chemical sciences ,QM/MM ,Solvent ,Colloid and Surface Chemistry ,Electric field ,Polar - Abstract
When and how do external electric fields (EEFs) lead to catalysis in the presence of a (polar or nonpolar) solvent? This is the question that is addressed here using a combination of molecular dynamics (MD) simulations, quantum mechanical/molecular mechanical calculations with EEF, and quantum mechanical/(local) electric field calculations. The paper focuses on a model reaction, the Menshutkin reaction between CH3I and pyridine in three solvents of varying polarity. Using MD simulations, we find that the EEF causes the solvent to undergo organization; the solvent molecules gradually align with the applied field as the field strength increases. The collective orientation of the solvent molecules modifies the electrostatic environment around the Menshutkin species and induces a global electric field pointing in the opposite direction of the applied EEF. The combination of these two entangled effects leads to partial or complete screening of the EEF, with the extent of screening being proportional to the polarity/polarizability of the solvent. Nevertheless, we find that catalysis of the Menshutkin reaction inevitably emerges once the EEF exceeds the opposing field of the organizing solvent, i.e., once polarization of the Menshutkin complex is observed to set in. Overall, our analysis provides a lucid and pictorial interpretation of the behavior of solutions in the presence of EEFs and indicates that EEF-mediated catalysis should, in principle, be feasible in bulk setups, especially for nonpolar and mildly polar solvents. By application of the charge-transfer paradigm, it is shown that the emergence of OEEF catalysis in solution can be generalized to other reactions as well.
- Published
- 2020
27. Oriented External Electric Fields and Ionic Additives Elicit Catalysis and Mechanistic Crossover in Oxidative Addition Reactions
- Author
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Sason Shaik, Thijs Stuyver, Jyothish Joy, Faculty of Sciences and Bioengineering Sciences, and General Chemistry
- Subjects
Chemistry ,Kinetics ,Crossover ,Ionic bonding ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Chemical reaction ,Oxidative addition ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Computational chemistry ,Electric field - Abstract
Judiciously applied oriented external electric fields (OEEFs) exert catalytic effects on the kinetics and improve the thermodynamics of chemical reactions. Herein, we examine the ability of OEEFs to assist catalysts and show that the rate of oxidative addition between palladium catalysts and alkyl/aryl electrophiles can be controlled by an OEEF applied along the direction of electron reorganization (the "reaction axis"). The concerted mechanism of oxidative addition proceeds through a transition state with moderate charge transfer character. We demonstrate that OEEFs along the reaction axis can control this charge transfer and impart electrostatic catalysis. When the applied field exceeds a certain critical value (∼0.15 V/Å), we observed a mechanistic crossover from the concerted to a dissociative CSNAr type of reactivity for aryl electrophiles. To our surprise, alkyl electrophiles follow a hitherto unexplored SN2 pathway for the reaction with large transition state stabilization at relatively low OEEFs. A valence-bond state correlation diagram (VBSCD) is employed to comprehend the results. Finally, although the catalytic effect of salt additives in oxidative addition is known, its mechanism is still under debate. Our findings further show evidence that salt additives exert electric-field effects on the rate of cross-coupling reactions, and their cocatalytic effects can be judiciously reproduced by applied external electric fields. As such, we propose that the use of additives (anionic or cationic) is an experimentally viable strategy to implement external electric-field effects in routinely used oxidative addition catalysis.
- Published
- 2020
28. Oriented (Local) Electric Fields Drive the Millionfold Enhancement of the H-Abstraction Catalysis Observed for Synthetic Metalloenzyme Analogues
- Author
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Rajeev Ramanan, Dibyendu Mallick, Sason Shaik, Thijs Stuyver, Faculty of Sciences and Bioengineering Sciences, and General Chemistry
- Subjects
010405 organic chemistry ,General Medicine ,General Chemistry ,Porphyrazine ,010402 general chemistry ,Electrostatics ,01 natural sciences ,Combinatorial chemistry ,Porphyrin ,Catalysis ,0104 chemical sciences ,Enzyme catalysis ,Abstraction (mathematics) ,chemistry.chemical_compound ,chemistry ,Electric field ,medicine ,Ferric ,medicine.drug - Abstract
This contribution follows the recent remarkable catalysis observed by Groves et al. in hydrogen-abstraction reactions by a) an oxoferryl porphyrin radical-cation complex [Por⋅+ FeIV (O)Lax ] and b) a hydroxoiron porphyrazine ferric complex [PyPzFeIII (OH)Lax ], both of which involve positively charged substituents on the outer circumference of the respective macrocyclic ligands. These charge-coronated complexes are analogues of the biologically important Compound I (Cpd I) and synthetic hydroxoferric species, respectively. We demonstrate that the observed enhancement of the H-abstraction catalysis for these systems is a purely electrostatic effect, elicited by the local charges embedded on the peripheries of the respective macrocyclic ligands. Our findings provide new insights into how electrostatics can be employed to tune the catalytic activity of metalloenzymes and can thus contribute to the future design of new and highly efficient hydrogen-abstraction catalysts.
- Published
- 2019
29. Do Diradicals Behave Like Radicals?
- Author
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Frank De Proft, Paul Geerlings, Bo Chen, Roald Hoffmann, Thijs Stuyver, Tao Zeng, Faculty of Sciences and Bioengineering Sciences, General Chemistry, Vriendenkring VUB, Quantum Chemistry - Molecular Modelling, and Chemistry
- Subjects
Spin states ,010405 organic chemistry ,Chemistry ,Diradical ,General Chemistry ,Electronic structure ,010402 general chemistry ,Hydrogen atom abstraction ,01 natural sciences ,0104 chemical sciences ,Delocalized electron ,Chemical physics ,Molecular orbital ,Singlet state ,Ground state - Abstract
This review sets out to understand the reactivity of diradicals and how that may differ from monoradicals. In the first part of the review, we delineate the electronic structure of a diradical with its two degenerate or nearly degenerate molecular orbitals, occupied by two electrons. A classification of diradicals based on whether or not the two SOMOs can be located on different sites of the molecule is useful in determining the ground state spin. Important is a delocalized to localized orbital transformation that interchanges "closed-shell" to "open-shell" descriptions. The resulting duality is useful in understanding the dual reactivity of singlet diradicals. In the second part of the review, we examine, with a consistent level of theory, activation energies of prototypical radical reactions (dimerization, hydrogen abstraction, and addition to ethylene) for representative organic diradicals and diradicaloids in their two lowest spin states. Differences and similarities in reactivity of diradicals vs monoradicals, based on either a localized or delocalized view, whichever is suitable, are then discussed. The last part of this review begins with an extensive, comparative, and critical survey of available measures of diradical character and ends with an analysis of the consequences of diradical character for selected diradicaloids.
- Published
- 2019
30. A Scandium‐Stabilized Diisophosphaethynolate Ligand: [OCPPCO] 4−
- Author
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Brian C. Manor, Lauren N. Grant, Hansjörg Grützmacher, Daniel J. Mindiola, Balazs Pinter, and General Chemistry
- Subjects
Chemistry(all) ,Ligand ,010405 organic chemistry ,OCP reduction ,scandium ,chemistry.chemical_element ,NacNac ,Phosphorus ,Phosphor ,General Chemistry ,Electronic structure ,General Medicine ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,NMR spectra database ,chemistry.chemical_compound ,Crystallography ,OCPPCO ,radical coupling ,chemistry ,Atomic orbital ,Scandium ,Single crystal - Abstract
The first example of the OCPPCO ligand, diisophosphaethynolate, is reported via reductive coupling of a Sc-OCP precursor. Upon reduction with KC8 , isolation of the dinuclear complex, namely [K(OEt2 )]2 [(nacnac)Sc(OAr)]2 (OCPPCO), is observed, leading to a unique motif [OCPPCO]4- , stabilized by two scandium centers. Detailed NMR spectra of all complexes as well as IR and single crystal X-ray studies were obtained to fully elucidate the nature of these complexes in solution as well as in the solid state. Theory is combined to probe the electronic structure and orbitals responsible for the bonding interactions in the Sc-OCPPCO-Sc skeleton but also to compare to the linear mode observed in the precursor.
- Published
- 2017
31. Exploiting the σ-Hole Concept: An Infrared and Raman-Based Characterization of the S⋅⋅⋅O Chalcogen Bond between 2,2,4,4-Tetrafluoro-1,3-dithiethane and Dimethyl Ether
- Author
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Frank De Proft, Freija De Vleeschouwer, Yannick Geboes, Wouter A. Herrebout, Chemistry, and General Chemistry
- Subjects
cryospectroscopy ,Chemistry(all) ,Dimer ,Inorganic chemistry ,Ab initio ,Infrared spectroscopy ,010402 general chemistry ,01 natural sciences ,Catalysis ,Chalcogen ,chemistry.chemical_compound ,symbols.namesake ,Ab initio quantum chemistry methods ,Non-covalent interactions ,Dimethyl ether ,chemistry.chemical_classification ,bond theory ,010405 organic chemistry ,Organic Chemistry ,General Chemistry ,0104 chemical sciences ,Chemistry ,Crystallography ,chemistry ,IR spectroscopy ,Raman spectroscopy ,chalcogens ,symbols ,NONCOVALENT INTERACTIONS - Abstract
In the last decade, halogen bonds, noncovalent interactions formed between positive regions in the electrostatic potential on halogen atoms, often referred to as sigma-holes, and electron-rich sites, have gained a lot of interest. Recently, this interest has been expanded towards interactions with GroupV and GroupVI elements, giving rise to pnicogen and chalcogen bonds. Although chalcogen bonds have already shown some promising results for applications in crystallography and catalysis, experimental results characterising these noncovalent interactions remain scarce. In this combined experimental and theoretical study, original data allowing the characterization of SO chalcogen bonds is obtained by studying the 1:1 molecular complexes between 2,2,4,4-tetrafluoro-1,3-dithiethane (C2F4S2) and dimethyl ether (DME). Ab initio calculations of the C2F4S2DME dimer yield two stable chalcogen-bonded isomers, the difference being the presence or absence of secondary FH interactions. Liquid-krypton solutions containing C2F4S2 and DME were studied using FTIR and Raman spectroscopy. Upon subtraction of rescaled monomer spectra, clear complex bands are observed. The observed complexation shifts agree favourably with the ab initio calculated shifts of the chalcogen-bonded complexes. The 1:1 stoichiometry of the complex is confirmed and a complexation enthalpy of -13.5(1)kJmol(-1) is found, which is in good agreement with the calculated values. A Ziegler-Rauk energy decomposition analysis revealed that electrostatic interactions prominently dominate over orbital interactions. Nevertheless, significant charge transfer occurs from the oxygen in DME to one of the sulfur atoms in C2F4S2 and the carbon along the extension of the chalcogen bond.
- Published
- 2017
32. Different Products of the Reduction of (N),C,N-Chelated Antimony(III) Compounds: Competitive Formation of Monomeric Stibinidenes versus 1H-2,1-Benzazastiboles
- Author
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Jan Turek, Roman Jambor, Mercedes Alonso, Iva Vránová, Aleš Růžička, Libor Dostál, Chemistry, Materials and Chemistry, and General Chemistry
- Subjects
Antimony ,heterocycles ,010405 organic chemistry ,Chemistry ,Ligand ,Reducing agent ,Dimer ,Organic Chemistry ,chemistry.chemical_element ,aromaticity ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,N ligands ,Monomer ,Organic chemistry ,Reactivity (chemistry) ,Chelation ,Stoichiometry ,Reduction - Abstract
The reduction of N,C,N-chelated antimony(III) chlorides [C 6H 3-2,6-(CH=NR) 2]SbCl 2(R=Ph (1), tBu (2), Dip (3); Dip=2,6-iPr 2C 6H 3) with an appropriate amount of KC 8or Li[AlH 4] resulted in the formation of rare examples of monomeric stibinidenes [C 6H 3-2,6-(CH=NR) 2]Sb (R=Ph (4), tBu (5), Dip (6)). Similarly, the reduction of compounds 1 or 2 by two equivalents of K[B(sBu) 3H] led to the stibinidenes 4 and 5. In contrast, the analogous reaction of compound 3 resulted in the formation of an unprecedented stibinidene [C 6H 3-2-(CH=NR)-6-(CH 2NHR)]Sb (7) (R=Dip), in which the hydrogen atoms that come from the K[B(sBu) 3H] are incorporated into the ligand backbone. To gain further insight into this intriguing reactivity with K[B(sBu) 3H] and to assess the influence of the substitution at both the antimony atom and pendant substituents, we prepared compounds [C 6H 3-2-(CH=NDip)]Sb(Ph)Cl (8) and [C 6H 2-2-(CH=NDip)-4,6-(tBu) 2]SbCl 2(9). The treatment of compound 8 with K[B(sBu) 3H] smoothly led to the 1-Ph-2-Dip-1H-2,1-benzazastibole (11), whereas the reaction of compound 9 with K[B(sBu) 3H] resulted in either tBu-substituted 1-Cl-2-Dip-1H-2,1-benzazastibole (13) or the formation of unprecedented Sb−Sb dimer bis(2-Dip-1H-2,1-benzazastibole) (12) depending on the reaction stoichiometry. The miscellaneous reactivity of antimony(III) precursors with reducing agents together with the structure and bonding of the resulting products has also been investigated from a theoretical point of view.
- Published
- 2017
33. Molecular titanium nitrides: nucleophiles unleashed
- Author
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Takashi Kurogi, Daniel J. Mindiola, Brian C. Manor, Balazs Pinter, Gang Wu, Lauren N. Grant, Maria E. Carroll, Patrick J. Carroll, and General Chemistry
- Subjects
Chemistry(all) ,010405 organic chemistry ,Dimer ,Inorganic chemistry ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,Resonance (chemistry) ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Crystallography ,Monomer ,chemistry ,Nucleophile ,Reactivity (chemistry) ,Azide ,Imide - Abstract
In this contribution we present reactivity studies of a rare example of a titanium salt, in the form of [μ 2-K(OEt 2)] 2[(PN) 2Ti≡N] 2 (1) (PN - = N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) to produce a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the latter, using various weak acids allowed us to narrow the pK a range of the NH group in (PN) 2Ti≡NH to be between 26-36. Complex 1 could be produced by a reductively promoted elimination of N 2 from the azide precursor (PN) 2TiN 3, whereas reductive splitting of N 2 could not be achieved using the complex (PN) 2Ti=N=N=Ti(PN) 2 (2) and a strong reductant. Complete N-atom transfer reactions could also be observed when 1 was treated with ClC(O) tBu and OCCPh2 to form NC tBu and KNCCPh 2, respectively, along with the terminal oxo complex (PN) 2Ti≡O, which was also characterized. A combination of solid state 15N NMR (MAS) and theoretical studies allowed us to understand the shielding effect of the counter cation in dimer 1, the monomer [K(18-crown-6)][(PN) 2Ti≡N], and the discrete salt [K(2,2,2-Kryptofix)][(PN) 2Ti≡N] as well as the origin of the highly downfield 15N NMR resonance when shifting from dimer to monomer to a terminal nitride (discrete salt). The upfield shift of 15N nitride resonance in the 15N NMR spectrum was found to be linked to the K + induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors.
- Published
- 2017
34. Synthesis and reactivity of a germylene stabilized by a boraguanidinate ligand
- Author
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Libor Dostál, Roman Jambor, Mercedes Alonso, Jiří Böserle, Aleš Růžička, Chemistry, and General Chemistry
- Subjects
Bromine ,010405 organic chemistry ,Ligand ,Stereochemistry ,General Chemical Engineering ,chemistry.chemical_element ,Germanium ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Dilithium ,Crystallography ,chemistry.chemical_compound ,chemistry ,Reactivity (chemistry) ,Diimine - Abstract
The germylene [(i-Pr)2NB(N-2,6-Me2C6H3)2]Ge (1) was easily accessible by the reaction of the in situ prepared dilithium precursor [(i-Pr)2NB(N-2,6-Me2C6H3)2]Li2 with GeCl2·dioxane complex. The bonding situation in 1 has been also described from the theoretical point of view. This germylene is smoothly oxidized by diphenyldichalcogenides PhEEPh, I2 or MeI to produce bis(phenylchalcogenato)germanes [(i-Pr)2NB(N-2,6-Me2C6H3)2]Ge(EPh)2 [where E = S (2), Se (3) and Te (4)] and corresponding iodo-derivatives [(i-Pr)2NB(N-2,6-Me2C6H3)2]GeI2 (5) and [(i-Pr)2NB(N-2,6-Me2C6H3)2]Ge(Me)I (6). The treatment of 1 with bromine resulted in the unexpected formation of a heteroleptic germylene compound [(i-Pr)2NB(NH-2,6-Me2C6H3)(N-2,6-Me2C6H3)]GeBr (7) and a germanium(IV) compound [(i-Pr)2NB(NH-2,6-Me2C6H3)(N-2,6-Me2C6H3)]GeBr3 (8). The reaction of germylene 1 with 2,3-dimethylbutadiene and 2,3-dibenzylbutadiene resulted in spiro-compounds [(i-Pr)2NB(N-2,6-Me2C6H3)2]Ge[CH2C(R)C(R)CH2] [where R = Me (10) and benzyl (11)]. Similarly, compound [(i-Pr)2NB(N-2,6-Me2C6H3)2]Ge[N(Dip)CHCHN(Dip)] (12) (where Dip = 2,6-i-Pr2C6H3) was obtained by the reaction of 1 with corresponding diimine (Dip)NCHCHN(Dip). All compounds were characterized by multinuclear NMR spectroscopy and their molecular structures were unambiguously established using single-crystal X-ray diffraction analysis.
- Published
- 2016
35. Characterization of hydroxylated amorphous silica: a numerical approach
- Author
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Nicholas W. Suek, Maxime Guillaume, Jean-Yves Delannoy, Frederik Tielens, Chemistry, and General Chemistry
- Subjects
Materials science ,Chemistry(all) ,General Chemical Engineering ,Monte Carlo method ,Ab initio ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Condensed Matter::Disordered Systems and Neural Networks ,Force field (chemistry) ,Adsorption ,Modeling ,General Chemistry ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,BET ,0104 chemical sciences ,Chemical physics ,silica ,TEM ,Chemical Engineering(all) ,Nanometre ,Amorphous silica ,0210 nano-technology ,BET theory - Abstract
Hydroxylated amorphous silica nanoparticles were modeled using a combination of computational techniques at different levels of length scales from Angstrom to hundreds of nanometers. Using quantum chemical ab initio methods, force field Monte Carlo methods, reactive force field simulations, and numerical model calculations, including BET theory calculations it was possible to describe and model the physico-chemical properties of hydroxylated amorphous silica. The results are compared with experimental data and found to be in good agreement with the theory, confirming the reliability of the computational method and the silica model structure.
- Published
- 2018
36. On the way of understanding the behavior of nanometer-scale metallic particles toward the adsorption of CO and NO molecules
- Author
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Frederik Tielens, Dominique Bazin, Chemistry, General Chemistry, Spectroscopie, Modélisation, Interfaces pour L'Environnement et la Santé (LCMCP-SMiLES), Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP), and Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Solid-state physics ,Chemistry(all) ,General Chemical Engineering ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,Heterogeneous catalysis ,01 natural sciences ,Catalysis ,no ,Metal ,chemistry.chemical_compound ,Adsorption ,Molecule ,activity ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,CO ,heterogeneous catalysis ,chemistry ,Chemical physics ,visual_art ,visual_art.visual_art_medium ,Chemical Engineering(all) ,Nanometre ,0210 nano-technology ,Carbon monoxide - Abstract
International audience; Previously, we have proposed a relationship between the adsorption modes of a simple molecule (NO) and the behavior of the nanometer-scale monometallic clusters after this adsorption. More precisely, a set of experiments seems to show that dissociative adsorption of NO leads to the sintering of nanometer-scale metallic particles (NSMPs), whereas molecular adsorption is related to the oxidation. Although numerous investigations have been published on catalytic or electrocatalytic reactions where the interaction between carbon monoxide and NSMPs is involved, only a few studies have been dedicated to the adsorption of CO on NSMPs. This purely energetic approach is discussed through different results already published in the literature and through some recent theoretical calculations related to solid state physics. Although interesting and systematic results are gathered here and are partly explained, this adsorption process still remains a challenge.
- Published
- 2018
37. A Terminal Iron(IV) Nitride Supported by a Super Bulky Guanidinate Ligand and Examination of Its Electronic Structure and Reactivity
- Author
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Jesse Murillo, Arnab Maity, Skye Fortier, Balazs Pinter, Alejandro J. Metta-Magaña, and General Chemistry
- Subjects
Absorption spectroscopy ,Chemistry(all) ,010405 organic chemistry ,Chemistry ,Ligand ,Tetrahedral molecular geometry ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Nitride ,010402 general chemistry ,Photochemistry ,Resonance (chemistry) ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Crystallography ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Azide ,HOMO/LUMO - Abstract
Utilizing the bulky guanidinate ligand [LAr*]− (LAr* = (Ar*N)2C(R), Ar* = 2,6-bis(diphenylmethyl)-4-tert-butylphenyl, R = NCtBu2) for kinetic stabilization, the synthesis of a rare terminal Fe(IV) nitride complex is reported. UV irradiation of a pyridine solution of the Fe(II) azide [LAr*]FeN3(py) (3-py) at 0 °C cleanly generates the Fe(IV) nitride [LAr*]FeN(py) (1). The 15N NMR spectrum of the 115N (50% Fe≡15N) isotopomer shows a resonance at 1016 ppm (vs externally referenced CH3NO2 at 380 ppm), comparable to that known for other terminal iron nitrides. Notably, the computed structure of 1 reveals an iron center with distorted tetrahedral geometry, τ4 = 0.72, featuring a short Fe≡N bond (1.52 Å). Inspection of the frontier orbital ordering of 1 shows a relatively small HOMO/LUMO gap with the LUMO comprised by Fe(dxz,yz)N(px,y) π*-orbitals, a splitting that is manifested in the electronic absorption spectrum of 1 (λ = 610 nm, ε = 1375 L·mol–1·cm–1; λ = 613 nm (calcd)). Complex 1 persists in low-temperature solutions of pyridine but becomes unstable at room temperature, gradually converting to the Fe(II) hydrazide product [κ2-(tBu2CN)C(η6-NAr*)(N-NAr*)]Fe (4) upon standing via intramolecular N-atom insertion. This reactivity of the Fe≡N moiety was assessed through molecular orbital analysis, which suggests electrophilic character at the nitride functionality. Accordingly, treatment of 1 with the nucleophiles PMe2Ph and Ar–N≡C (Ar = 2,6-dimethylphenyl) leads to partial N-atom transfer and formation of the Fe(II) addition products [LAr*]Fe(N═PMe2Ph)(py) (5) and [LAr*]Fe(N═C═NAr)(py) (6). Similarly, 1 reacts with PhSiH3 to give [LAr*]Fe[N(H)(SiH2Ph)](py) (7) which Fukui analysis shows to proceed via electrophilic insertion of the nitride into the Si–H bond.
- Published
- 2017
38. Bonding in Heavier Group 14 Zero-Valent Complexes-A Combined Maximum Probability Domain and Valence Bond Theory Approach
- Author
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Benoît Braïda, Jan Turek, Frank De Proft, Chemistry, and General Chemistry
- Subjects
Group 14 elements ,Chemistry(all) ,010405 organic chemistry ,Chemistry ,Ligand ,ab initio calculations ,Organic Chemistry ,Bent molecular geometry ,General Chemistry ,010402 general chemistry ,Resonance (chemistry) ,01 natural sciences ,bonding ,Catalysis ,0104 chemical sciences ,Crystallography ,chemistry.chemical_compound ,Atomic orbital ,Computational chemistry ,maximum probability domains ,valence bond theory ,Valence bond theory ,Carbene ,Lone pair ,Natural bond orbital - Abstract
The bonding in heavier Group 14 zero-valent complexes of a general formula L2 E (E=Si-Pb; L=phosphine, N-heterocyclic and acyclic carbene, cyclic tetrylene and carbon monoxide) is probed by combining valence bond (VB) theory and maximum probability domain (MPD) approaches. All studied complexes are initially evaluated on the basis of the structural parameters and the shape of frontier orbitals revealing a bent structural motif and the presence of two lone pairs at the central E atom. For the VB calculations three resonance structures are suggested, representing the "ylidone", "ylidene" and "bent allene" structures, respectively. The influence of both ligands and central atoms on the bonding situation is clearly expressed in different weights of the resonance structures for the particular complexes. In general, the bonding in the studied E0 compounds, the tetrylones, is best described as a resonating combination of "ylidone" and "ylidene" structures with a minor contribution of the "bent allene" structure. Moreover, the VB calculations allow for a straightforward assessment of the π-backbonding (E→L) stabilization energy. The validity of the suggested resonance model is further confirmed by the complementary MPD calculations focusing on the E lone pair region as well as the E-L bonding region. Likewise, the MPD method reveals a strong influence of the σ-donating and π-accepting properties of the ligand. In particular, either one single domain or two symmetrical domains are found in the lone pair region of the central atom, supporting the predominance of either the "ylidene" or "ylidone" structures having one or two lone pairs at the central atom, respectively. Furthermore, the calculated average populations in the lone pair MPDs correlate very well with the natural bond orbital (NBO) populations, and can be related to the average number of electrons that is backdonated to the ligands.
- Published
- 2017
39. Conceptual Insights into DFT Spin-State Energetics of Octahedral Transition-Metal Complexes through a Density Difference Analysis
- Author
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Jeremy N. Harvey, Balazs Pinter, Paul Geerlings, Frank De Proft, Artiom Chankisjijev, Chemistry, General Chemistry, and Quantum Chemistry - Molecular Modelling
- Subjects
Electron density ,010304 chemical physics ,Spin states ,Electronic correlation ,Chemistry(all) ,Chemistry ,Organic Chemistry ,Ionic bonding ,General Chemistry ,Electronic structure ,electron correlation ,exact exchange admixture ,010402 general chemistry ,spin-state energetics ,01 natural sciences ,Catalysis ,transition metals ,0104 chemical sciences ,d electron count ,Transition metal ,Chemical physics ,Computational chemistry ,0103 physical sciences ,density functional calculations ,Density functional theory - Abstract
In this study, an intuitive concept is derived, which explains the characteristic dependence of spin-state energetics on the exact exchange admixture of DFT functionals in the case of octahedral transition metal complexes. The change in electron density distributions upon varying the admixture, c 3, in the B3LYP functional is analyzed for archetype ionic and covalent systems as well as for the Fe 2+ ion in an ideal octahedral field. An understanding of how the DFT description of the electronic structure of octahedral complexes changes as a function of c 3 is sought. A systematic spin-state energy analysis of 50 octahedral complexes of various metals and ligands with consistent experimental data is presented, allowing the derivation, in theory, of an optimal c 3 value for each system. The notion that the admixture dependence of DFT spin-state energetics stems from the treatment of nondynamic electrons arising from the mixing of (M–L z2) 0(d z2) 2 and (M–L x2-y2 0(d( x2-y2)) 2 configurations into the dominant (M–L x2-y2) 2(d x2-y2) 0 and (M–L x2-y2) 2(d x2-y2) 0 ones in the low(er) spin states is put forward. That is, in the effort to mimic such electron–electron interactions, E x LDA overestimates, whereas exact exchange downplays the contribution of this type of electron correlation to the stability of low(er) spin states, leading to the widespread practical observation that the higher the exact exchange admixture, the more stable the high-spin-state configuration.
- Published
- 2017
40. Revealing the thermodynamic driving force for ligand-based reductions in quinoids; conceptual rules for designing redox active and non-innocent ligands
- Author
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F. De Proft, Gabriella Skara, Balazs Pinter, Paul Geerlings, General Chemistry, and Chemistry
- Subjects
DFT, thermodynamic ,Ligand ,Stereochemistry ,Critical factors ,chemistry.chemical_element ,General Chemistry ,Overpotential ,Redox ,Non-innocent ligand ,Ruthenium ,Electron transfer ,chemistry ,Computational chemistry ,Redox active - Abstract
Metal and ligand-based reductions have been modeled in octahedral ruthenium complexes revealing metal–ligand interactions as the profound driving force for the redox-active behaviour of orthoquinoid-type ligands. Through an extensive investigation of redox-active ligands we revealed the most critical factors that facilitate or suppress redox-activity of ligands in metal complexes, from which basic rules for designing non-innocent/redox-active ligands can be put forward. These rules also allow rational redox-leveling, i.e. the moderation of redox potentials of ligand-centred electron transfer processes, potentially leading to catalysts with low overpotential in multielectron activation processes.
- Published
- 2015
41. Characterization of chalcogen bonding interactions via an in-depth conceptual quantum chemical analysis
- Author
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Balazs Pinter, Mats Denayer, Frank De Proft, Paul Geerlings, Freija De Vleeschouwer, Chemistry, General Chemistry, Faculty of Sciences and Bioengineering Sciences, Quantum Chemistry - Molecular Modelling, and Vriendenkring VUB
- Subjects
Electron density ,Valence (chemistry) ,Chemistry(all) ,010405 organic chemistry ,Hydrogen bond ,Chemistry ,Atoms in molecules ,General Chemistry ,010402 general chemistry ,energy decomposition analysis ,noncovalent interaction ,01 natural sciences ,0104 chemical sciences ,chalcogen-bonding ,Computational Mathematics ,Chalcogen ,Computational chemistry ,Chemical physics ,HSAB theory ,Density functional theory ,density functional theory ,σ-hole ,Fukui function - Abstract
The chalcogen bond has been acknowledged as an influential noncovalent interaction (NCI) between an electron-deficient chalcogen (donor) and a Lewis base (acceptor). This work explores the main features of chalcogen bonding through a large-scale computational study on a series of donors and acceptors spanning a wide range in strength and character of this type of bond: (benzo)chalcogenadiazoles (with Ch = Te/Se/S) versus halides and neutral Lewis bases with O, N, and C as donor atoms. We start from Pearson's hard and soft acids and bases (HSAB) principle, where the hard nature of the chalcogen bond is quantified through the molecular electrostatic potential and the soft nature through the Fukui function. The σ-holes are more pronounced when going down in the periodic table and their directionality matches the structural orientation of donors and acceptors in the complexes. The Fukui functions point toward an n→σ*-type interaction. The initial conjectures are further scrutinized using quantum mechanical methods, mostly relating to the systems' electron density. A Ziegler–Rauk energy decomposition analysis shows that electrostatics plays a distinctly larger role for the soft halides than for the hard, uncharged acceptors, associated with the softness matching within the HSAB principle. The natural orbital for chemical valence analysis confirms the n→σ* electron donation mechanism. Finally, the electron density and local density energy at the bond critical point in the quantum theory of atoms in molecules study and the position of the spikes in the reduced density gradient versus density plot in the NCI theory situate the chalcogen bond in the same range as strong hydrogen bonds. © 2017 Wiley Periodicals, Inc.
- Published
- 2017
42. Rational Design of Nanobody80 Loop Peptidomimetics
- Author
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Cecilia Betti, Els Pardon, Daniel Sejer Pedersen, May C. Morris, Samuel L. C. Moors, Krisztina Fehér, Jesper Mosolff Mathiesen, Jan Steyaert, Mia Danielsen, Frank De Proft, Cecilia Fabris, Nick Devoogdt, Marion Peyressatre, Vicky Caveliers, Charlotte Martin, Steven Ballet, José C. Martins, Chemistry, WE Academic Unit, Department of Bio-engineering Sciences, Faculty of Sciences and Bioengineering Sciences, Structural Biology Brussels, Translational Imaging Research Alliance, Medical Imaging, Supporting clinical sciences, General Chemistry, Vrije Universiteit Brussel (VUB), University of Copenhagen = Københavns Universitet (KU), Department of Drug Design and Pharmacology [Copenhagen] (ILF), Faculty of Health and Medical Sciences, University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), VIB-VUB Center for Structural Biology [Bruxelles], VIB [Belgium], Institut des Biomolécules Max Mousseron [Pôle Chimie Balard] (IBMM), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Department of Organic and Macromolecular Chemistry, Universiteit Gent = Ghent University [Belgium] (UGENT), NMR and Structure Analysis Unit, In vivo Cellular and Molecular Imaging Laboratory, and Eenheid Algemene Chemie
- Subjects
0301 basic medicine ,Protein-protein interactions ,Stereochemistry ,G protein ,Peptidomimetic ,receptors ,Plasma protein binding ,protein–protein interactions ,01 natural sciences ,Catalysis ,Protein–protein interaction ,03 medical and health sciences ,MESH: Receptors, Adrenergic, Beta-2 / metabolism ,Protein structure ,[SDV.BBM]Life Sciences [q-bio]/Biochemistry, Molecular Biology ,Binding site ,G protein-coupled receptor ,MESH: Optical Imaging ,MESH: Peptidomimetics / chemical synthesis ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Rational design ,MESH: Single-Domain Antibodies / chemistry ,General Chemistry ,nanobodies ,0104 chemical sciences ,030104 developmental biology ,MESH: HEK293 Cells ,peptidomimetics ,protein structures ,[SDV.IB]Life Sciences [q-bio]/Bioengineering - Abstract
International audience; G protein-coupled receptors (GPCRs) play an important role in many cellular responses; as such, their mechanism of action is of utmost interest. To gain insight into the active conformation of GPCRs, the X-ray crystal structures of nanobody (Nb)-stabilized β2 -adrenergic receptor (β2 AR) have been reported. Nb80, in particular, is able to bind the intracellular G protein binding site of β2 AR and stabilize the receptor in an active conformation. Within Nb80, the complementarity-determining region 3 (CDR3) is responsible for most of the binding interactions. Hence, we hypothesized that peptidomimetics of the CDR3 loop might be sufficient for binding to the receptor, inhibiting the interaction of β2 AR with intracellular GPCR interacting proteins (e.g., G proteins). Based on previous crystallographic data, a set of peptidomimetics were synthesized that, similar to the Nb80 CDR3 loop, adopt a β-hairpin conformation. Syntheses, conformational analysis, binding and functional in vitro assays, as well as internalization experiments, were performed. We demonstrate that peptidomimetics can structurally mimic the CDR3 loop of a nanobody and its function by inhibiting G protein coupling as measured by partial inhibition of cAMP production.
- Published
- 2017
43. A Planar Ti2P2 Core Assembled by Reductive Decarbonylation of −O−C≡P and P−P Radical Coupling
- Author
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Brian C. Manor, Daniel J. Mindiola, Hansjörg Grützmacher, Riccardo Suter, Lauren N. Grant, Balazs Pinter, Chemistry, and General Chemistry
- Subjects
Chemistry(all) ,NacNac ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,Ion ,chemistry.chemical_compound ,Planar ,Transition metal ,Atom ,titanium ,010405 organic chemistry ,Organic Chemistry ,Decarbonylation ,P-2 ,Phosphorus ,General Chemistry ,P-4 ,Resonance (chemistry) ,aryloxide ,0104 chemical sciences ,Bond length ,Crystallography ,chemistry ,phosphaethynolate - Abstract
The first structural elucidation of the first group 4 transition metal P2 complex, namely [(nacnac)Ti(OAr)]2(μ2:η2,η2-P2) (1), is reported. Complex 1 is formed via reductive decarbonylation of the phosphaethynolate ion -[OCP], which serves as a P atom source. The rhombic Ti2P2 core is essentially planar with short bond lengths suggesting some degree of multiple bonding character between the Ti-P and P-P sites. Also observed in 1 was the rather downfield shifted 31P NMR spectroscopic signal, appearing as a broadened resonance (Δν1/2 ~ 4034 Hz) at 907 ppm. Computational studies of 1 provide an understanding of the Ti2P2 core as well as the origin of the highly downfield 31P NMR spectroscopic signal.
- Published
- 2017
44. Comparison of reactivity of C,N-chelated and Lappert’s stannylenes with trimethylsilylazide
- Author
-
RůžičkaAleš, ŠvecPetr, AlonsoMercedes, De ProftFrank, PadělkováZdeňka, General Chemistry, and Chemistry
- Subjects
chemistry ,Stereochemistry ,Reactivity of C,N-chelated and Lappert’s Stannylen ,Organic Chemistry ,chemistry.chemical_element ,Reactivity (chemistry) ,Chelation ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Tin ,Medicinal chemistry ,Catalysis - Abstract
Two mixed amido-azido tin(IV) species bearing either C,N-chelating or bulky amido ligands were prepared by the reaction of the corresponding stannylene (e.g., Sn[N(SiMe3)2]2 (1) or (LCN)2Sn (2, LCN = 2-(N,N-dimethylaminomethyl)phenyl)) with Me3SiN3. Both products of the oxidative addition, Sn[N(SiMe3)2]3N3 (3) and (LCN)2Sn[N(SiMe3)2]N3 (5), respectively, were fully characterized by both multinuclear NMR spectroscopy and XRD analysis. Heating of a mixture of 2 and Me3SiN3 up to 100 °C lead to the formation of a novel dimeric species (LCN)2Sn(μ-NSiMe3)2Sn(LCN)2 (4), where the two tin atoms are bridged by two NSiMe3 ligands, thus forming a four-membered diazadistannacycle. DFT calculations were also carried out to support the proposed reaction mechanisms.
- Published
- 2014
45. Aromatic sulfonation with sulfur trioxide: mechanism and kinetic model
- Author
-
Samuel L. C. Moors, Frank De Proft, Xavier Deraet, Guy Van Assche, Paul Geerlings, Chemistry, Faculty of Sciences and Bioengineering Sciences, Physical Chemistry and Polymer Science, Materials and Chemistry, General Chemistry, and Quantum Chemistry - Molecular Modelling
- Subjects
Chemistry(all) ,010405 organic chemistry ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Solvent ,Aromatic sulfonation ,chemistry.chemical_compound ,Chemistry ,chemistry ,Solvent models ,Electrophile ,Elementary reaction ,Sulfur trioxide ,Molecule ,Benzene - Abstract
Electrophilic aromatic sulfonation of benzene with sulfur trioxide is studied with ab initio molecular dynamics simulations in gas phase, and in explicit noncomplexing (CCl3F) and complexing (CH3NO2) solvent models., Electrophilic aromatic sulfonation of benzene with sulfur trioxide is studied with ab initio molecular dynamics simulations in gas phase, and in explicit noncomplexing (CCl3F) and complexing (CH3NO2) solvent models. We investigate different possible reaction pathways, the number of SO3 molecules participating in the reaction, and the influence of the solvent. Our simulations confirm the existence of a low-energy concerted pathway with formation of a cyclic transition state with two SO3 molecules. Based on the simulation results, we propose a sequence of elementary reaction steps and a kinetic model compatible with experimental data. Furthermore, a new alternative reaction pathway is proposed in complexing solvent, involving two SO3 and one CH3NO2.
- Published
- 2016
46. Back Cover
- Author
-
Frederik Tielens, Miguel Monge, Françoise Remacle, María Rodríguez-Castillo, Gustavo Lugo-Preciado, Yannick Guari, Arie van der Lee, Sébastien Richeter, Danielle Laurencin, Sébastien Clément, José M. López-de-Luzuriaga, and General Chemistry
- Subjects
Benzimidazole ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Nanoparticle ,General Chemistry ,gold ,010402 general chemistry ,01 natural sciences ,DFT ,Catalysis ,0104 chemical sciences ,carbenes ,Surface ,chemistry.chemical_compound ,Colloidal gold ,Polymer chemistry ,Cover (algebra) ,Reactivity (chemistry) ,nanoparticles - Published
- 2016
47. Spontaneous Double Hydrometallation Induced by N ® M Coordination in Organometallic Hydrides of Group 14 Elements
- Author
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Mercedes Alonso, Frank De Proft, Aleš Růžička, Libor Dostál, Miroslav Novák, Jan Turek, Roman Jambor, Chemistry, and General Chemistry
- Subjects
Carbon group ,010405 organic chemistry ,Chemistry ,Ligand ,Stereochemistry ,Hydride ,Organic Chemistry ,Imine ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Crystallography ,Intramolecular force ,Homoleptic - Abstract
Our attempts to synthesise N→M intramolecularly coordinated diorganometallic hydrides L2MH2 [M=Si (4), Ge (5), Sn (6)] containing the CH=N imine group (in which L is C,N-chelating ligand {2-[(2,6-iPr2C6H3)N=CH]C6 H4}(-)) yielded 1,1'-bis(2,6-diisopropylphenyl)-2,2'-spriobi[benzo[c][1,2]azasilole] (7), 1,1'-bis(2,6-diisopropylphenyl)-2,2'-spriobi[benzo[c][1,2]azagermole] (8) and C,N-chelated homoleptic stannylene L2Sn (10), respectively. Compounds 7 and 8 are an outcome of a spontaneous double hydrometallation of the two CH=N imine moieties induced by N→M intramolecular coordination (M=Si, Ge) in the absence of any catalyst. In contrast, the diorganotin hydride L2SnH2 (6) is redox-unstable and the reduction of the tin centre with the elimination of H2 provided the C,N-chelated homoleptic stannylene L2Sn (10). Compounds 7 and 8 were characterised by NMR spectroscopy and X-ray diffraction analysis. Because the proposed N→M intramolecularly coordinated diorganometallic hydrides L2MH2 [M=Si (4), Ge (5), Sn (6)] revealed two different types of reduction reactions, DFT calculations were performed to gain an insight into the structures and bonding of the non-isolable diorganometallic hydrides as well as the products of their subsequent reactions. Furthermore, the thermodynamic profiles of the different reaction pathways with respect to the central metal atom were also investigated.
- Published
- 2016
48. Correlation Corrections to the Molecular Dipole Moment of Closed Shell Molecules via Møller-Plesset Perturbation Theory
- Author
-
C. Van Alsenoy, H. P. Figeys, Paul Geerlings, General Chemistry, and Vrije Universiteit Brussel
- Subjects
Moment (mathematics) ,Dipole ,Chemistry ,Quantum mechanics ,Quantum electrodynamics ,Møller–Plesset perturbation theory ,Transition dipole moment ,Physics::Atomic and Molecular Clusters ,Unrestricted Hartree–Fock ,General Chemistry ,Perturbation theory ,Open shell ,Spin-½ - Abstract
Using Moller-Plesset perturbation theory a general expression is derived for the second order correlation corrections to the molecular dipole moment obtained via a Spin Unrestricted Hartree Fock procedure. It is shown that this expression can be considerably simplified in the case of a closed-shell molecule. The final result is computationally attractive.
- Published
- 2010
49. Local Aromaticity of Pristine and Fluorinated Carbon Nanotubes
- Author
-
Miquel Torrent-Sucarrat, Christopher P. Ewels, Miquel Solà, Paul Geerlings, Van Lier G, Sílvia Osuna, Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Chemistry, and General Chemistry
- Subjects
Nanotube ,Materials science ,Chemical shift ,Biomedical Engineering ,Bioengineering ,Aromaticity ,02 engineering and technology ,General Chemistry ,Carbon nanotube ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Curvature ,01 natural sciences ,0104 chemical sciences ,law.invention ,local aromaticity ,Chemical physics ,law ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Molecule ,General Materials Science ,Physics::Chemical Physics ,0210 nano-technology - Abstract
International audience; We examine the use of nucleus independent chemical shifts (NICS) as a tool for analysis of pristine and fluorinated finite-length carbon nanotubes. The introduction of both variable molecule length and different nanotube curvatures introduces additional subtleties to NICS analysis not present in analysis of more conventional 2D molecules. Notably the precise length of tube segment considered can strongly influence calculated NICS values. We provide specific examples using (6,6) and (7, 7) nanotube segments under fluorination. Although care should be taken when comparing systems of different length or curvature, important chemical information can still be retrieved from the local aromaticity patterns. In particular, local aromaticity is observed to play a relevant role in the orientation towards the ideal C4F addition pattern for fluorinated carbon nanotubes.
- Published
- 2009
50. Metalated Hexaphyrins: From Understanding to Rational Design
- Author
-
Frank De Proft, Paul Geerlings, Balazs Pinter, Mercedes Alonso, General Chemistry, and Chemistry
- Subjects
Quantum chemical ,Metalation ,Chemistry ,Ligand ,Organic Chemistry ,Rational design ,Aromaticity ,General Chemistry ,Catalysis ,Effective nuclear charge ,Key factors ,Computational chemistry ,Organic chemistry ,Metalated Hexaphyrins ,Molecular topology - Abstract
The heretofore unpredictable behavior of [26] and [28]hexaphyrins upon metalation has been elucidated through quantum chemical calculations. It is demonstrated that the molecular topology of Group 10 and Group 11 metal complexes of hexaphyrins depends on sensitive interplay between the intrinsic ligand strain and the metal–ligand interaction strength. As such, the aromaticity of the ligand and effective charge of the metal are revealed as key factors determining the binding mode and the preference for Möbius or Hückel structures. These findings offer a new perspective to rationalize experimental observations for metalated hexaphyrins. More importantly, the proposed guidelines could be useful for designing novel complexes of hexaphyrins, such as a hitherto unknown Möbius [26]hexaphyrin complex.
- Published
- 2015
Catalog
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