37 results on '"Varinia Bernales"'
Search Results
2. Computational Design of Functionalized Metal–Organic Framework Nodes for Catalysis
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Varinia Bernales, Manuel A. Ortuño, Donald G. Truhlar, Christopher J. Cramer, and Laura Gagliardi
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Chemistry ,QD1-999 - Abstract
Recent progress in the synthesis and characterization of metal–organic frameworks (MOFs) has opened the door to an increasing number of possible catalytic applications. The great versatility of MOFs creates a large chemical space, whose thorough experimental examination becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide experimental efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion.
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- 2017
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3. Metal–Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature
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Zhanyong Li, Aaron W. Peters, Varinia Bernales, Manuel A. Ortuño, Neil M. Schweitzer, Matthew R. DeStefano, Leighanne C. Gallington, Ana E. Platero-Prats, Karena W. Chapman, Christopher J. Cramer, Laura Gagliardi, Joseph T. Hupp, and Omar K. Farha
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Chemistry ,QD1-999 - Published
- 2016
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4. Rhodium catalyzed hydroformylation of olefins.
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Varinia Bernales and Robert D. Froese
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- 2019
- Full Text
- View/download PDF
5. Polyethylene crosslinking using the epoxy‐anhydride reaction I: A strategy for a curing process with high thermal sensitivity
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Kevin Lawry, Varinia Bernales, Jeffrey Cogen, Daniel Davies, Kyoungmoo Koh, John Kramer, Dakai Ren, Mark Rickard, Tanya Singh‐Rachford, Yabin Sun, and Thomas Peterson
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Organic Chemistry ,Physical and Theoretical Chemistry - Published
- 2022
6. The role of cations in uranyl nanocluster association: a molecular dynamics study
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Varinia Bernales, Edward J. Maginn, Ken Newcomb, Laura Gagliardi, and Surya Prakash Tiwari
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chemistry.chemical_classification ,Aqueous solution ,General Physics and Astronomy ,Uranyl ,Peroxide ,Ion ,Nanoclusters ,Divalent ,chemistry.chemical_compound ,Molecular dynamics ,Crystallography ,chemistry ,Cluster (physics) ,Physical and Theoretical Chemistry - Abstract
Actinyl ions can self-assemble in aqueous solution to form closed cage clusters ranging from 1.5 to 4.0 nm in diameter. The self-assembly, stability, and behavior of the nanoclusters depend on the nature of the aqueous environment, such as the pH and cations present. In this work, a classical force field for [(UO2)20(O2)30]20- (U20) peroxide nanoclusters in aqueous solution was developed from quantum-mechanical calculations. Using molecular dynamics simulations, the preferred binding sites of six cations (Li+, Na+, K+, Rb+, Cs+, and Ca2+) to the nanocluster were determined. Replica exchange molecular dynamics was used to equilibrate the structure and determine the equilibrium distribution of cations and water with respect to the nanocluster cage. In addition, the free energy barriers associated with cations entering the cluster were computed. Finally, the association of two cages was investigated by computing the free energy as a function of intercage distance. The free energy profiles reveal that the nanoclusters prefer to be associated when neutralized with divalent cations, but do not associate when neutralized with monovalent cations. This could explain the formation of tertiary structures observed experimentally.
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- 2020
7. Enhanced Fe-Centered Redox Flexibility in Fe–Ti Heterobimetallic Complexes
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Shengfa Ye, Connie C. Lu, Kyle M. Lancaster, Laura Gagliardi, Maxime Tarrago, Varinia Bernales, James T. Moore, Sudipta Chatterjee, Laura J. Clouston, Stephen Sproules, and Eckhard Bill
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X-ray absorption spectroscopy ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,010402 general chemistry ,01 natural sciences ,Redox ,Article ,3. Good health ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Crystallography ,law ,Mössbauer spectroscopy ,Density functional theory ,Physical and Theoretical Chemistry ,Cyclic voltammetry ,Isostructural ,Electron paramagnetic resonance - Abstract
Previously, we reported the synthesis of Ti[N(o-(NCH2P(iPr)2)C6H4)3] and the Fe–Ti complex, FeTi[N(o-(NCH2P(iPr)2)C6H4)3], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe–Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at −2.16 and −1.36 V (versus Fc/Fc+), respectively. Two isostructural redox members, [FeTiL]+ and [FeTiL]− (2ox and 2red, respectively) were synthesized and characterized, along with BrFeTiL (2-Br) and the monometallic [TiL]+ complex (1ox). The solid-state structures of the [FeTiL]+/0/– series feature short metal–metal bonds, ranging from 1.94–2.38 Å, which are all shorter than the sum of the Ti and Fe single-bond metallic radii (cf. 2.49 Å). To elucidate the bonding and electronic structures, the complexes were characterized with a host of spectroscopic methods, including NMR, EPR, and 57Fe Mössbauer, as well as Ti and Fe K-edge X-ray absorption spectroscopy (XAS). These studies, along with hybrid density functional theory (DFT) and time-dependent DFT calculations, suggest that the redox processes in the isostructural [FeTiL]+,0,– series are primarily Fe-based and that the polarized Fe–Ti π-bonds play a role in delocalizing some of the additional electron density from Fe to Ti (net 13%)., An isostructural redox series of Fe≡Ti complexes was investigated using a combination of spectroscopic methods and density functional theory to elucidate their electronic structures and to understand their polarized metal−metal bonding. Overall, the results support that the redox changes occur primarily at the Fe site though some electron density is delocalized to Ti. Hence, the Ti plays an important role in enhancing the redox flexibility of the single Fe site.
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- 2019
8. Negative cooperativity upon hydrogen bond-stabilized O2 adsorption in a redox-active metal-organic framework
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Harriet Li, Benjamin A. Trump, Jeffrey R. Long, Douglas A. Reed, Laura Gagliardi, Kristen A. Colwell, Henry Z. H. Jiang, Craig M. Brown, Julia Oktawiec, Varinia Bernales, Lucy E. Darago, Jenny G. Vitillo, and Hiroyasu Furukawa
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Coordination sphere ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,Photochemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,Metal ,Electron transfer ,Adsorption ,Electronic effect ,lcsh:Science ,Multidisciplinary ,Hydrogen bond ,General Chemistry ,Metal-organic frameworks ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,visual_art ,visual_art.visual_art_medium ,Metal-organic framework ,lcsh:Q ,Materials chemistry ,0210 nano-technology ,Cobalt ,Inorganic chemistry - Abstract
The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O2 carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal–organic framework Co2(OH)2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) leads to strong and reversible adsorption of O2. In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O2 adsorption. Notably, O2-binding in this material weakens as a function of loading, as a result of negative cooperativity arising from electronic effects within the extended framework lattice. This unprecedented behavior extends the tunable properties that can be used to design metal–organic frameworks for adsorption-based applications., Oxygen capture is attractive for catalysis, sensing, and separations, but engineering stable and selective adsorbents is challenging. Here the authors combine metal-based electron transfer with secondary coordination sphere effects in a metal-organic framework, leading to strong and reversible O2 adsorption that also exhibits negative cooperativity.
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- 2020
9. Rhodium catalyzed hydroformylation of olefins
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Robert D. J. Froese and Varinia Bernales
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Olefin fiber ,Ethylene ,010304 chemical physics ,Ligand ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Rhodium ,Catalysis ,Computational Mathematics ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Carbonylation ,Hydroformylation ,Carbon monoxide - Abstract
DFT and CCSD(T) methods were used to examine 61 different rhodium catalysts for the hydroformylation of ethylene. The carbon monoxide (CO) stretching frequency was a key electronic parameter to understand the π-accepting nature of the ligand. Normally, π-accepting ligands lead to increased CO stretching frequencies and a reduction in CO dissociation energy. There was no relationship between CO dissociation energy and CO stretching frequency. However, a clear relationship exists between the ethylene insertion barrier (from the rhodium dicarbonyl hydride resting state) and the CO stretching frequency as stronger π-accepting ligands systematically led to a reduction in the barrier. Due to the multistep nature of the rate-limiting step, the overall barrier can be divided into the CO/ethylene equilibrium and an intrinsic ethylene insertion barrier and both are systematically reduced as the π-accepting nature of the ligand is increased. A comparison of the carbonylation transition state (TS) to the ethylene insertion TS allowed us to understand reversibility of olefin insertion. While the ethylene insertion TS systematically decreases with increasing CO stretching frequency, the carbonylation TS is relatively flat. The lines cross at 2156 cm-1 implying a change in the rate-limiting step in this region given a standard set of process conditions. © 2018 Wiley Periodicals, Inc.
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- 2018
10. Catalytic descriptors and electronic properties of single-site catalysts for ethene dimerization to 1-butene
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Rachel B. Getman, Peilin Liao, Randall Q. Snurr, Steven Pellizzeri, Melissa Barona, Laura Gagliardi, Varinia Bernales, and Pere Miró
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Metal hydroxide ,Hydrogen ,010405 organic chemistry ,chemistry.chemical_element ,1-Butene ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Metal ,chemistry.chemical_compound ,Adsorption ,Transition metal ,chemistry ,visual_art ,visual_art.visual_art_medium ,Physical chemistry ,Metal-organic framework - Abstract
Six first-row transition metal cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) were evaluated as catalysts for ethene dimerization to 1-butene. This is an important reaction in the chemistry of C C bond formation and in the conversion of natural gas to higher hydrocarbons. Two related classes of transition metal cation catalysts were investigated: 1) single transition metal cations supported on zirconium oxide nodes of the metal–organic framework NU-1000 and 2) small metal hydroxide clusters with two metal atoms (M2) that could be grown by atomic layer deposition on a support exhibiting isolated hydroxyl groups. Using scaling relations, the free energies of co-adsorbed hydrogen and ethene (i.e., (H/C2H4)*) and adsorbed ethyl (i.e., C2H5*) were identified as descriptors for ethene dimerization catalysis. Using degree of rate control analysis, it was determined that the rate controlling steps are either ethene insertion (C C bond forming) or β-hydride elimination (C H bond breaking), depending on the metal. Using degree of catalyst control analysis, it was determined that activity on all the catalysts studied could be improved by tuning the free energy of C2H5*.
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- 2018
11. C–H Bond Activation on Bimetallic Two-Atom Co-M Oxide Clusters Deposited on Zr-Based MOF Nodes: Effects of Doping at the Molecular Level
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Christopher J. Cramer, Laura Gagliardi, Aditya Bhan, Matthew C. Simons, Varinia Bernales, Manuel A. Ortuño, and Carlo Alberto Gaggioli
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Materials science ,Dopant ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Partial charge ,chemistry.chemical_compound ,chemistry ,Atom ,Cluster (physics) ,Physical chemistry ,Metal-organic framework ,Density functional theory ,0210 nano-technology ,Cobalt - Abstract
Cluster-based density functional theory calculations show that energy barriers for the dissociative adsorption of propane on two-cation, Co-M oxide clusters supported on Zr-based nodes of NU-1000, a metal–organic framework material, vary from 57 to 9 kcal mol–1 based on the identity of the dopant. Systematic changes in spin density and positive partial charge on oxygen atoms bridging the two metal atoms (Co–O-M) are noted upon addition of dopants to cobalt, with increasing values of both giving lower enthalpic barriers to C–H scission. These observed correlations can be rationalized in terms of concepts applicable to bulk systems and provide target materials for synthesis.
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- 2018
12. Structure and Dynamics of Zr6O8 Metal–Organic Framework Node Surfaces Probed with Ethanol Dehydration as a Catalytic Test Reaction
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Bruce C. Gates, Christopher J. Cramer, Laura Gagliardi, Manuel A. Ortuño, Varinia Bernales, and Dong Yang
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Ethylene ,010405 organic chemistry ,Chemistry ,Oxide ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Metal ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,visual_art ,visual_art.visual_art_medium ,SN2 reaction ,Metal-organic framework ,Density functional theory ,Diethyl ether - Abstract
Some metal–organic frameworks (MOFs) incorporate nodes that are metal oxide clusters such as Zr6O8. Vacancies on the node surfaces, accidental or by design, act as catalytic sites. Here, we report elucidation of the chemistry of Zr6O8 nodes in the MOFs UiO-66 and UiO-67 having used infrared and nuclear magnetic resonance spectroscopies to determine the ligands on the node surfaces originating from the solvents and modifiers used in the syntheses and having elucidated the catalytic properties of the nodes for ethanol dehydration, which takes place selectively to make diethyl ether but not ethylene at 473–523 K. Density functional theory calculations show that the key to the selective catalysis is the breaking of node-linker bonds (or the accidental adjacency of open/defect sites) that allows catalytically fruitful bonding of the reactant ethanol to neighboring sites on the nodes, facilitating the bimolecular ether formation through an SN2 mechanism.
- Published
- 2018
13. Bridging Zirconia Nodes within a Metal–Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires
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Alice Dohnalkova, Donald G. Truhlar, B. Layla Mehdi, Aaron B. League, Leighanne C. Gallington, Varinia Bernales, Karena W. Chapman, John L. Fulton, Omar K. Farha, Johannes A. Lercher, Ana E. Platero-Prats, Laura Gagliardi, Joseph T. Hupp, Donald M. Camaioni, Jingyun Ye, Nigel D. Browning, Zhanyong Li, Christopher J. Cramer, Andrew Stevens, Jian Zheng, Aleksei Vjunov, Mahalingam Balasubramanian, and Neil M. Schweitzer
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Nanostructure ,Bridging (networking) ,Absorption spectroscopy ,Chemistry ,Nanowire ,Pair distribution function ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Atomic layer deposition ,Colloid and Surface Chemistry ,Cubic zirconia ,0210 nano-technology - Abstract
Metal–organic frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for preparing well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, atomic layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is critical to understanding how these components couple to govern the active material properties. By combining local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function analysis, and difference envelope density analysis, with electron microscopy imaging and computational modeling, we resolve the precise atomic structure of metal-oxo species deposited in the MOF NU-1000 through ALD. These analyses demonstrate that deposition of NiOxHy clusters occurs selectively ...
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- 2017
14. Molecular Rhodium Complexes Supported on the Metal-Oxide-Like Nodes of Metal Organic Frameworks and on Zeolite HY: Catalysts for Ethylene Hydrogenation and Dimerization
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Christopher J. Cramer, Jun Yu, Gamze Gümüşlü, Bruce C. Gates, Laura Gagliardi, Dong Yang, and Varinia Bernales
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Reaction mechanism ,Ethylene ,Materials science ,010405 organic chemistry ,Inorganic chemistry ,Oxide ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Rhodium ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Physical chemistry ,General Materials Science ,Metal-organic framework ,Zeolite - Abstract
Metal–organic frameworks (MOFs) with nodes consisting of zirconium oxide clusters (Zr6) offer new opportunities as supports for catalysts with well-defined, essentially molecular, structures. We used the precursor Rh(C2H4)2(acac) (acac is acetylacetonate) to anchor Rh(I) complexes to the nodes of the MOF UiO-67 and, for comparison, to the zeolite dealuminated HY (DAY). These were characterized experimentally by measurement of catalytic activities and selectivities for ethylene hydrogenation and dimerization in a once-through flow reactor at 298 K and 1 bar. The catalyst performance data are complemented with structural information determined by infrared and extended X-ray absorption fine structure spectroscopies and by calculations at the level of density functional theory, the latter carried out also to extend the investigation to a related MOF, NU-1000. The agreement between the experimental and calculated structural metrics is good, and the calculations have led to predictions of reaction mechanisms an...
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- 2017
15. Atomic Layer Deposition in a Metal–Organic Framework: Synthesis, Characterization, and Performance of a Solid Acid
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Martino Rimoldi, Christopher J. Cramer, Laura Gagliardi, John L. Fulton, Johannes A. Lercher, Leighanne C. Gallington, Karena W. Chapman, Varinia Bernales, In Soo Kim, Omar K. Farha, Joshua Borycz, Joseph T. Hupp, Aleksei Vjunov, Ana E. Platero-Prats, and Alex B. F. Martinson
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Zirconium ,Extended X-ray absorption fine structure ,Chemistry ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,Atomic layer deposition ,Chemical engineering ,Materials Chemistry ,Density functional theory ,Metal-organic framework ,0210 nano-technology ,Mesoporous material ,Selectivity - Abstract
NU-1000, a zirconium-based metal–organic framework (MOF) featuring mesoporous channels, has been postsynthetically metalated via atomic layer deposition in a MOF (AIM) employing dimethylaluminum iso-propoxide ([AlMe2OiPr]2, DMAI), a milder precursor than widely used trimethylaluminum (AlMe3, TMA). The aluminum-modified NU-1000 (Al-NU-1000) has been characterized with a comprehensive suite of techniques that points to the formation of aluminum oxide clusters well dispersed through the framework and stabilized by confinement within small pores intrinsic to the NU-1000 structure. Experimental evidence allows for identification of spectroscopic similarities between Al-NU-1000 and γ-Al2O3. Density functional theory modeling provides structures and simulated spectra, the relevance of which can be assessed via comparison to experimental IR and EXAFS data. The catalytic performance of Al-NU-1000 has been benchmarked against γ-Al2O3, with promising results in terms of selectivity.
- Published
- 2017
16. Computationally-Guided Assignment of Unexpected Signals in the Raman Spectra of Uranyl Triperoxide Complexes
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Mateusz Dembowski, Sarah Hickam, Laura Gagliardi, Varinia Bernales, Jie Qiu, Gabriel Gaspar, and Peter C. Burns
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Aqueous solution ,010405 organic chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Electronic structure ,Uranium ,010402 general chemistry ,Uranyl ,01 natural sciences ,Peroxide ,0104 chemical sciences ,Inorganic Chemistry ,Isotopic labeling ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Uranyl peroxide ,symbols ,Physical chemistry ,Physical and Theoretical Chemistry ,Raman spectroscopy - Abstract
Combination of uranium, peroxide, and mono- (Na, K) or divalent (Mg, Ca, Sr) cations under alkaline aqueous conditions results in the rapid formation of anionic uranyl triperoxide monomers (UTs), (UO2(O2)3)4–, exhibiting unique Raman signatures. Electronic structure calculations were decisive for the interpretation of the spectra and assignment of unexpected signals associated with vibrations of the uranyl and peroxide ions. Assignments were verified by 18O isotopic labeling of the uranyl ions supporting the computational-based interpretation of the experimentally observed peaks and the assignment of a novel asymmetric vibration of the peroxide ligands, v2(O22–).
- Published
- 2017
17. Metal–Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature
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Christopher J. Cramer, Leighanne C. Gallington, Ana E. Platero-Prats, Joseph T. Hupp, Varinia Bernales, Omar K. Farha, Laura Gagliardi, Karena W. Chapman, Neil M. Schweitzer, Matthew R. DeStefano, Zhanyong Li, Manuel A. Ortuño, and Aaron W. Peters
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010405 organic chemistry ,Chemistry ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Heterogeneous catalysis ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,3. Good health ,Catalysis ,lcsh:Chemistry ,Propene ,chemistry.chemical_compound ,lcsh:QD1-999 ,Chemical engineering ,Propane ,Dehydrogenation ,Metal-organic framework ,Mesoporous material ,Cobalt ,Research Article - Abstract
Zr-based metal–organic frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Additionally, their crystalline nature affords the opportunity for molecular level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6 nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and atomic layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, respectively. The location of the deposited Co species in the two materials is determined via difference envelope density (DED) analysis. Upon activation in a flow of O2 at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same experimental conditions due to differences in the Co species generated in these two materials upon activation as observed by in situ X-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the observed catalytic activity at low temperature., Metal−organic framework supported cobalt oxides catalyze the oxidative dehydrogenation of propane with high propene selectivity at low temperature.
- Published
- 2016
18. Tuning the Surface Chemistry of Metal Organic Framework Nodes: Proton Topology of the Metal-Oxide-Like Zr6 Nodes of UiO-66 and NU-1000
- Author
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Christopher J. Cramer, Laura Gagliardi, Varinia Bernales, Timur Islamoglu, Joseph T. Hupp, Bruce C. Gates, Omar K. Farha, and Dong Yang
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Chemistry ,Metal ions in aqueous solution ,Inorganic chemistry ,Oxide ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Metal ,Crystallography ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,visual_art ,Vacancy defect ,Alkoxy group ,visual_art.visual_art_medium ,Metal-organic framework ,Density functional theory ,0210 nano-technology ,Topology (chemistry) - Abstract
Some metal organic frameworks (MOFs) incorporate nodes that are nanoscale metal oxides, and the hydroxy-containing functional groups on them provide opportunities for introducing catalytic sites with precisely defined structures. Investigations have been done to understand the structures of these groups on nodes and node vacancies, because, in prospect, atomic-scale modulation of the composition, areal density, and/or siting of the groups would open up possibilities for exquisite tuning of the siting and performance of subsequently anchored catalytic units (e.g., single metal ions, pairs of metal ions, or well-defined metal-ion-containing clusters). We have combined infrared (IR) spectroscopy and density functional theory (DFT) to demonstrate tuning of these sites, namely, hydrogen-bonded OH/OH2 groups on the Zr6 nodes of the MOFs UiO-66 and NU-1000 via the intermediacy of node methoxy (or ethoxy) groups formed from methanol (or ethanol). Methoxy (or ethoxy) groups on node vacancy sites are converted to a...
- Published
- 2016
19. Density matrix renormalization group pair-density functional theory (DMRG-PDFT): singlet-triplet gaps in polyacenes and polyacetylenes
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Stefan Knecht, Laura Gagliardi, Donald G. Truhlar, Prachi Sharma, and Varinia Bernales
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Physics ,Chemical Physics (physics.chem-ph) ,Condensed Matter::Quantum Gases ,Field (physics) ,010405 organic chemistry ,High Energy Physics::Lattice ,Density matrix renormalization group ,Multireference configuration interaction ,FOS: Physical sciences ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Chemistry ,Quantum mechanics ,Physics - Chemical Physics ,Condensed Matter::Statistical Mechanics ,Density functional theory ,Condensed Matter::Strongly Correlated Electrons ,Limit (mathematics) ,Singlet state ,Perturbation theory ,Wave function - Abstract
The density matrix renormalization group (DMRG) is a powerful method to treat static correlation. Here we present an inexpensive way to calculate correlation energy starting from a DMRG wave function using pair-density functional theory (PDFT). We applied this new approach, called DMRG-PDFT, to study singlet–triplet gaps in polyacenes and polyacetylenes that require active spaces larger than the feasibility limit of the conventional complete active-space self-consistent field (CASSCF) method. The results match reasonably well with the most reliable literature values and have only a moderate dependence on the compression of the initial DMRG wave function. Furthermore, DMRG-PDFT is significantly less expensive than other commonly applied ways of adding additional correlation to DMRG, such as DMRG followed by multireference perturbation theory or multireference configuration interaction., Chemical Science, 10 (6), ISSN:2041-6520, ISSN:2041-6539
- Published
- 2019
20. Valence ππ* Excitations in Benzene Studied by Multiconfiguration Pair-Density Functional Theory
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Prachi Sharma, Laura Gagliardi, Varinia Bernales, and Donald G. Truhlar
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Physics ,Valence (chemistry) ,010304 chemical physics ,Ionic bonding ,010402 general chemistry ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Covalent bond ,0103 physical sciences ,General Materials Science ,Density functional theory ,Complete active space ,Singlet state ,Physical and Theoretical Chemistry ,Scaling ,Excitation - Abstract
We explore the valence singlet and triplet ππ* excitations of benzene with complete active pace self-consistent field (CASSCF) theory, complete active space perturbation theory (CASPT2), and multiconfiguration pair-density functional theory (MC-PDFT) for four different choices of active space. We propose a new way to quantify the covalent and ionic character of the electronic states in terms of the components of the total electronic energy. We also explore the effect of scaling the exchange and correlation components of the on-top density functional used in MC-PDFT; we observe that increasing the exchange contribution improves the MC-PDFT excitation energies for benzene.
- Published
- 2018
21. Computational Study of First-Row Transition Metals Supported on MOF NU-1000 for Catalytic Acceptorless Alcohol Dehydrogenation
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Manuel A. Ortuño, Laura Gagliardi, Christopher J. Cramer, and Varinia Bernales
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Chemistry ,Alcohol ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,General Energy ,Transition metal ,Chemical engineering ,Organic chemistry ,Density functional theory ,Dehydrogenation ,Physical and Theoretical Chemistry ,0210 nano-technology ,Mesoporous material ,Hydrogen production - Abstract
Metal–organic frameworks (MOF) are a versatile family of mesoporous materials that can be used as solid supports to design well-defined catalytic sites. Herein we employ density functional theory (DFT) to evaluate first-row transition metals deposited on the MOF NU-1000 for acceptorless alcohol dehydrogenation, a reaction of great interest in hydrogen production and storage. The proposed mechanism reveals that the MOF support plays an active role in proton-transfer processes. The computational screening of first-row transition metals highlights Ni- and Co-derivatives as potential catalysts for the title reaction.
- Published
- 2016
22. Computationally Guided Discovery of a Catalytic Cobalt-Decorated Metal–Organic Framework for Ethylene Dimerization
- Author
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Omar K. Farha, Joseph T. Hupp, Varinia Bernales, Rebecca K. Carlson, Neil M. Schweitzer, Zhanyong Li, Laura Gagliardi, Aaron B. League, Christopher J. Cramer, and Aaron W. Peters
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Ethylene ,Materials science ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Combinatorial chemistry ,Transition state ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,Nickel ,General Energy ,chemistry ,Transition metal ,Metal-organic framework ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Cobalt - Abstract
The catalytic performance of a cobalt(II) single-site catalyst supported on the zirconia-like nodes of the metal organic–framework (MOF) NU-1000 is herein characterized by quantum chemical methods and compared to an iso-structural analogue incorporating nickel(II) as the active transition metal. The mechanisms of atomic layer deposition in MOFs and of catalysis are examined using density functional theory. We compare the catalytic activity of Co and Ni installed on the zirconia-like nodes for ethylene dimerization, considering three plausible pathways. Multiconfigurational wave function theory methods are employed to further characterize the electronic structures of key transition states and intermediates. Finally, we report confirmation of Co catalytic activity for ethylene dimerization from experiments that were prompted by the computational prediction.
- Published
- 2016
23. Installing Heterobimetallic Cobalt–Aluminum Single Sites on a Metal Organic Framework Support
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Varinia Bernales, Leighanne C. Gallington, Sai Puneet Desai, Stephen J. Tereniak, Dale R. Pahls, Joseph T. Hupp, Laura Gagliardi, In Soo Kim, Omar K. Farha, Andreas Stein, Timothy C. Wang, Anthony B. Thompson, R. Lee Penn, Camille D. Malonzo, Connie C. Lu, Thomas E. Webber, Zhanyong Li, Karena W. Chapman, and Alex B. F. Martinson
- Subjects
Materials science ,Chemical substance ,Ligand ,General Chemical Engineering ,Oxide ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Materials Chemistry ,Cluster (physics) ,Metal-organic framework ,0210 nano-technology ,Science, technology and society ,Bimetallic strip ,Cobalt - Abstract
A heterobimetallic cobalt–aluminum complex was immobilized onto the metal organic framework NU-1000 using a simple solution-based deposition procedure. Characterization data are consistent with a maximum loading of a single Co–Al complex per Zr6 node of NU-1000. Furthermore, the data support that the Co–Al bimetallic complex is evenly distributed throughout the NU-1000 particle, binds covalently to the Zr6 nodes, and occupies the NU-1000 apertures with the shortest internode distances (∼8.5 A). Heating the anchored Co–Al complex on NU-1000 at 300 °C for 1 h in air completely removes the organic ligand of the complex without affecting the structural integrity of the MOF support. We propose that a Co–Al oxide cluster is formed in place of the anchored complex in NU-1000 during heating. Collectively, the results suggest that well-defined heterobimetallic complexes can be effective precursors for installing two different metals simultaneously onto a MOF support. The CoAl-functionalized NU-1000 samples catalyz...
- Published
- 2016
24. Can Density Matrix Embedding Theory with the Complete Activate Space Self-Consistent Field Solver Describe Single and Double Bond Breaking in Molecular Systems?
- Author
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Laura Gagliardi, Hung Q. Pham, and Varinia Bernales
- Subjects
Chemical Physics (physics.chem-ph) ,Density matrix ,Physics ,010304 chemical physics ,FOS: Physical sciences ,Solver ,01 natural sciences ,Computer Science Applications ,Embedding problem ,Quantum mechanics ,Lattice (order) ,Physics - Chemical Physics ,0103 physical sciences ,Embedding ,Single bond ,Complete active space ,Physical and Theoretical Chemistry ,010306 general physics ,Quantum - Abstract
Density matrix embedding theory (DMET) [Phys. Rev. Lett.2012, 109, 186404] has been demonstrated as an efficient wave-function-based embedding method to treat extended systems. Despite its success in many quantum lattice models, the extension of DMET to real chemical systems has been tested only on selected cases. Herein, we introduce the use of the complete active space self-consistent field (CASSCF) method as a correlated impurity solver for DMET, leading to a method called CAS-DMET. We test its performance in describing the dissociation of a H-H single bond in a H10 ring model system and an N=N double bond in azomethane (CH3-N=N-CH3) and pentyldiazene (CH3(CH2)4-N=NH). We find that the performance of CAS-DMET is comparable to CASSCF with different active space choices when single-embedding DMET corresponding to only one embedding problem for the system is used. When multiple embedding problems are used for the system, the CAS-DMET is in a good agreement with CASSCF for the geometries around the equilibrium, but not in equal agreement at bond dissociation., 28 pages, 9 figures, TOC graphic
- Published
- 2017
25. Catalytic Silylation of Dinitrogen with a Dicobalt Complex
- Author
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Varinia Bernales, Laura J. Clouston, Connie C. Lu, Laura Gagliardi, Nora Planas, Randall B. Siedschlag, Eckhard Bill, and Konstantinos D. Vogiatzis
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biology ,Trimethylsilyl ,Silylation ,Active site ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Biochemistry ,Catalysis ,Turnover number ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Catalytic cycle ,biology.protein ,Amine gas treating ,Cobalt - Abstract
A dicobalt complex catalyzes N2 silylation with Me3SiCl and KC8 under 1 atm N2 at ambient temperature. Tris(trimethylsilyl)amine is formed with an initial turnover rate of 1 N(TMS)3/min, ultimately reaching a turnover number of ∼200. The dicobalt species features a metal-metal interaction, which we postulate is important to its function. Although N2 functionalization occurs at a single cobalt site, the second cobalt center modifies the electronics at the active site. Density functional calculations reveal that the Co-Co interaction evolves during the catalytic cycle: weakening upon N2 binding, breaking with silylation of the metal-bound N2 and reforming with expulsion of [N2(SiMe3)3](-).
- Published
- 2015
26. Computational Design of Functionalized Metal-Organic Framework Nodes for Catalysis
- Author
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Laura Gagliardi, Christopher J. Cramer, Varinia Bernales, Donald G. Truhlar, and Manuel A. Ortuño
- Subjects
Computer science ,General Chemical Engineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chemical space ,0104 chemical sciences ,Characterization (materials science) ,Catalysis ,lcsh:Chemistry ,lcsh:QD1-999 ,Key (cryptography) ,Computational design ,Metal-organic framework ,0210 nano-technology ,Outlook - Abstract
Recent progress in the synthesis and characterization of metal–organic frameworks (MOFs) has opened the door to an increasing number of possible catalytic applications. The great versatility of MOFs creates a large chemical space, whose thorough experimental examination becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide experimental efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion., We discuss computational design of catalytic materials by taking advantage of the capability of metal−organic frameworks (MOFs) to combine the advantages of homogeneous and heterogeneous catalysts.
- Published
- 2017
27. Uranyl Peroxide Cage Cluster Solubility in Water and the Role of the Electrical Double Layer
- Author
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Jennifer E. S. Szymanowski, Laura Gagliardi, Enrica Balboni, Varinia Bernales, Sarah Hickam, Haylie L. Lobeck, Christine M. Wallace, Mateusz Dembowski, Kristi L. Pellegrini, Kathryn M. Peruski, Peter C. Burns, and Ginger E. Sigmon
- Subjects
Chemistry ,Inorganic chemistry ,Close-packing of equal spheres ,chemistry.chemical_element ,02 engineering and technology ,Uranium ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Uranyl ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Hydrolysis ,Uranyl peroxide ,Cluster (physics) ,Physical and Theoretical Chemistry ,Solubility ,0210 nano-technology ,Cage - Abstract
Uranium concentrations as high as 2.94 × 105 parts per million (1.82 mol of U/1 kg of H2O) occur in water containing nanoscale uranyl cage clusters. The anionic cage clusters, with diameters of 1.5–2.5 nm, are charge-balanced by encapsulated cations, as well as cations within their electrical double layer in solution. The concentration of uranium in these systems is impacted by the countercations (K, Li, Na), and molecular dynamics simulations have predicted their distributions in selected cases. Formation of uranyl cages prevents hydrolysis reactions that would result in formation of insoluble uranyl solids under alkaline conditions, and these spherical clusters reach concentrations that require close packing in solution.
- Published
- 2017
28. Tuning the Surface Chemistry of Metal Organic Framework Nodes: Proton Topology of the Metal-Oxide-Like Zr
- Author
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Dong, Yang, Varinia, Bernales, Timur, Islamoglu, Omar K, Farha, Joseph T, Hupp, Christopher J, Cramer, Laura, Gagliardi, and Bruce C, Gates
- Abstract
Some metal organic frameworks (MOFs) incorporate nodes that are nanoscale metal oxides, and the hydroxy-containing functional groups on them provide opportunities for introducing catalytic sites with precisely defined structures. Investigations have been done to understand the structures of these groups on nodes and node vacancies, because, in prospect, atomic-scale modulation of the composition, areal density, and/or siting of the groups would open up possibilities for exquisite tuning of the siting and performance of subsequently anchored catalytic units (e.g., single metal ions, pairs of metal ions, or well-defined metal-ion-containing clusters). We have combined infrared (IR) spectroscopy and density functional theory (DFT) to demonstrate tuning of these sites, namely, hydrogen-bonded OH/OH
- Published
- 2016
29. Unprecedented selectivity in molecular recognition of carbohydrates by a metal-organic framework
- Author
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Omar K. Farha, Atsushi Fukuoka, Mizuho Yabushita, Laura Gagliardi, Peng Li, Alexander Katz, Hirokazu Kobayashi, and Varinia Bernales
- Subjects
Surface Properties ,Carbohydrates ,02 engineering and technology ,Cellobiose ,010402 general chemistry ,01 natural sciences ,Catalysis ,chemistry.chemical_compound ,Molecular recognition ,Adsorption ,Materials Chemistry ,Organic chemistry ,Metal-Organic Frameworks ,Aqueous solution ,fungi ,Metals and Alloys ,General Chemistry ,021001 nanoscience & nanotechnology ,Combinatorial chemistry ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Monomer ,Glucose ,chemistry ,Ceramics and Composites ,Pyrene ,Metal-organic framework ,0210 nano-technology ,Selectivity - Abstract
Metal-organic framework (MOF) material NU-1000 adsorbs dimers cellobiose and lactose from aqueous solution, in amounts exceeding 1250 mg gNU-1000(-1) while completely excluding the adsorption of the monomer glucose, even in a competitive mode with cellobiose. The MOF also discriminates between dimers consisting of α and β linkages, showing no adsorption of maltose. Electronic structure calculations demonstrate that key to this selective molecular recognition is the number of favorable CH-π interactions made by the sugar with pyrene units of the MOF.
- Published
- 2016
30. Sintering-Resistant Single-Site Nickel Catalyst Supported by Metal-Organic Framework
- Author
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Christopher J. Cramer, Aaron W. Peters, Aleksei Vjunov, John L. Fulton, Joseph T. Hupp, Zhanyong Li, Jeffrey T. Miller, Varinia Bernales, Aaron B. League, Andrew 'Bean' Getsoian, Laura Gagliardi, Omar K. Farha, Johannes A. Lercher, Neil M. Schweitzer, and Timothy C. Wang
- Subjects
Models, Molecular ,Chemical substance ,chemistry.chemical_element ,Sintering ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,Heterogeneous catalysis ,01 natural sciences ,Biochemistry ,Catalysis ,Atomic layer deposition ,Colloid and Surface Chemistry ,Nickel ,Organic Chemicals ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,X-Ray Absorption Spectroscopy ,chemistry ,Chemical engineering ,Metal-organic framework ,Hydrogenation ,0210 nano-technology ,Science, technology and society - Abstract
Developing supported single-site catalysts is an important goal in heterogeneous catalysis since the well-defined active sites afford opportunities for detailed mechanistic studies, thereby facilitating the design of improved catalysts. We present herein a method for installing Ni ions uniformly and precisely on the node of a Zr-based metal-organic framework (MOF), NU-1000, in high density and large quantity (denoted as Ni-AIM) using atomic layer deposition (ALD) in a MOF (AIM). Ni-AIM is demonstrated to be an efficient gas-phase hydrogenation catalyst upon activation. The structure of the active sites in Ni-AIM is proposed, revealing its single-site nature. More importantly, due to the organic linker used to construct the MOF support, the Ni ions stay isolated throughout the hydrogenation catalysis, in accord with its long-term stability. A quantum chemical characterization of the catalyst and the catalytic process complements the experimental results. With validation of computational modeling protocols, we further targeted ethylene oligomerization catalysis by Ni-AIM guided by theoretical prediction. Given the generality of the AIM methodology, this emerging class of materials should prove ripe for the discovery of new catalysts for the transformation of volatile substrates.
- Published
- 2016
31. Structural and Spectroscopic Characterization of Reaction Intermediates Involved in a Dinuclear Co-Hbpp Water Oxidation Catalyst
- Author
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Alexander A. Guda, Nora Planas, Laia Francàs, Isidoro López, Varinia Bernales, Carolina Gimbert-Suriñach, Lorenzo Mognon, Asmaul Hoque, Antoni Llobet, Dooshaye Moonshiram, Christopher J. Cramer, Fernando Bozoglian, and Laura Gagliardi
- Subjects
010405 organic chemistry ,Chemistry ,General Chemistry ,Reaction intermediate ,010402 general chemistry ,Resonance (chemistry) ,Photochemistry ,01 natural sciences ,Biochemistry ,Redox ,Catalysis ,Transition state ,0104 chemical sciences ,law.invention ,Crystallography ,Colloid and Surface Chemistry ,Catalytic cycle ,Catalytic oxidation ,law ,TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY ,Electron paramagnetic resonance - Abstract
An end-on superoxido complex with the formula {[CoIII(OH2)(trpy)][CoIII(OO•)(trpy)](μ-bpp)}4+ (34+) (bpp– = bis(2-pyridyl)-3,5-pyrazolate; trpy = 2,2′;6′:2″-terpyridine) has been characterized by resonance Raman, electron paramagnetic resonance, and X-ray absorption spectroscopies. These results together with online mass spectrometry experiments using 17O and 18O isotopically labeled compounds prove that this compound is a key intermediate of the water oxidation reaction catalyzed by the peroxido-bridged complex {[CoIII(trpy)]2(μ-bpp)(μ-OO)}3+ (13+). DFT calculations agree with and complement the experimental data, offering a complete description of the transition states and intermediates involved in the catalytic cycle.
- Published
- 2016
32. Quantum Mechanical Continuum Solvation Models for Ionic Liquids
- Author
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Christopher J. Cramer, Varinia Bernales, Renato Contreras, Aleksandr V. Marenich, and Donald G. Truhlar
- Subjects
Models, Molecular ,Hydrogen bond ,Implicit solvation ,Solvation ,Ionic Liquids ,Thermodynamics ,Hydrogen Bonding ,Surfaces, Coatings and Films ,Solvent ,chemistry.chemical_compound ,Solvation shell ,chemistry ,Ionic liquid ,Solvents ,Materials Chemistry ,Quantum Theory ,Physical chemistry ,Free energies ,Physical and Theoretical Chemistry ,Quantum - Abstract
The quantum mechanical SMD continuum universal solvation model can be applied to predict the free energy of solvation of any solute in any solvent following specification of various macroscopic solvent parameters. For three ionic liquids where these descriptors are readily available, the SMD solvation model exhibits a mean unsigned error of 0.48 kcal/mol for 93 solvation free energies of neutral solutes and a mean unsigned error of 1.10 kcal/mol for 148 water-to-IL transfer free energies. Because the necessary solvent parameters are not always available for a given ionic liquid, we determine average values for a set of ionic liquids over which measurements have been made in order to define a generic ionic liquid solvation model, SMD-GIL. Considering 11 different ionic liquids, the SMD-GIL solvation model exhibits a mean unsigned error of 0.43 kcal/mol for 344 solvation free energies of neutral solutes and a mean unsigned error of 0.61 kcal/mol for 431 water-to-IL transfer free energies. As these errors are similar in magnitude to those typically observed when applying continuum solvation models to ordinary liquids, we conclude that the SMD universal solvation model may be applied to ionic liquids as well as ordinary liquids.
- Published
- 2012
33. Heterobimetallic Complexes That Bond Vanadium to Iron, Cobalt, and Nickel
- Author
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Laura Gagliardi, Varinia Bernales, Rebecca K. Carlson, Ryan C. Cammarota, Laura J. Clouston, Eckhard Bill, and Connie C. Lu
- Subjects
Inorganic chemistry ,chemistry.chemical_element ,Vanadium ,Magnetic susceptibility ,law.invention ,Inorganic Chemistry ,Bond length ,Crystallography ,Nickel ,chemistry ,law ,Mössbauer spectroscopy ,Molecule ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Cobalt - Abstract
Zero-valent iron, cobalt, and nickel were installed into the metalloligand V[N(o-(NCH2P((i)Pr)2)C6H4)3] (1, VL), generating the heterobimetallic trio FeVL (2), CoVL (3), and NiVL (4), respectively. In addition, the one-electron-oxidized analogues [FeVL]X ([2(ox)]X, where X(-) = BPh4 or PF6) and [CoVL]BPh4 ([3(ox)]BPh4) were prepared. The complexes were characterized by a host of physical methods, including cyclic voltammetry, X-ray crystallography, magnetic susceptibility, electronic absorption, NMR, electron paramagnetic resonance (EPR), and Mössbauer spectroscopies. The CoV and FeV heterobimetallic compounds have short M-V bond lengths that are consistent with M-M multiple bonding. As revealed by theoretical calculations, the M-V bond is triple in 2, 2(ox), and 3(ox), double in 3, and dative (Ni → V) in 4. The (d-d)(10) species, 2 and 3(ox), are diamagnetic and exhibit large diamagnetic anisotropies of -4700 × 10(-36) m(3)/molecule. Complexes 2 and 3(ox) are also characterized by intense visible bands at 760 and 610 nm (ε1000 M(-1) cm(-1)), respectively, which correspond to an intermetal (M → V) charge-transfer transition. Magnetic susceptibility measurements and EPR characterization establish S = (1)/2 ground states for (d-d)(9) 2(ox) and (d-d)(11) 3, while (d-d)(12) 4 is S = 1 based on Evans' method.
- Published
- 2015
34. Bimetallic cobalt-dinitrogen complexes: impact of the supporting metal on N2 activation
- Author
-
Laura J. Clouston, Varinia Bernales, Rebecca K. Carlson, Laura Gagliardi, and Connie C. Lu
- Subjects
Ligand ,Stereochemistry ,chemistry.chemical_element ,Infrared spectroscopy ,Inorganic Chemistry ,Bond length ,Metal ,Crystallography ,chemistry ,Transition metal ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Isostructural ,Bimetallic strip ,Cobalt - Abstract
Expanding a family of cobalt bimetallic complexes, we report the synthesis of the Ti(III) metalloligand, Ti[N(o-(NCH2P((i)Pr)2)C6H4)3] (abbreviated as TiL), and three heterobimetallics that pair cobalt with an early transition metal ion: CoTiL (1), K(crypt-222)[(N2)CoVL] (2), and K(crypt-222)[(N2)CoCrL] (3). The latter two complexes, along with previously reported K(crypt-222)[(N2)CoAlL] and K(crypt-222)[(N2)Co2L], constitute an isostructural series of cobalt bimetallics that bind dinitrogen in an end-on fashion, i.e. [(N2)CoML](-). The characterization of 1-3 includes cyclic voltammetry, X-ray crystallography, and infrared spectroscopy. The [CoTiL](0/-) reduction potential is extremely negative at -3.20 V versus Fc(+)/Fc. In the CoML series where M is a transition metal, the reduction potentials shift anodically as M is varied across the first-row period. Among the [(N2)CoML](-) compounds, the dinitrogen ligand is weakly activated, as evidenced by N-N bond lengths between 1.110(8) and 1.135(4) Å and by N-N stretching frequencies between 1971 and 1995 cm(-1). Though changes in νN2 are subtle, the extent of N2 activation decreases across the first-row period. A correlation is found between the [CoML](0/-) reduction potentials and N2 activation, where the more cathodic potentials correspond to lower N-N frequencies. Theoretical calculations of the [(N2)CoML](-) complexes reveal important variations in the electronic structure and Co-M interactions, which depend on the exact nature of the supporting metal ion, M.
- Published
- 2015
35. Isobutane as a probe of the structure of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids
- Author
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Laure Pison, Patricio Fuentealba, Varinia Bernales, Margarida F. Costa Gomes, Agilio A. H. Padua, Institut de Chimie de Clermont-Ferrand (ICCF), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-SIGMA Clermont (SIGMA Clermont)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Departamento de Química, Facultad de Ciencias, Universidad de Chile, Santiago, Departamento de Fisica [USACH Santiago], and Universidad de Santiago de Chile [Santiago] (USACH)
- Subjects
Inorganic chemistry ,02 engineering and technology ,Gas solubility ,010402 general chemistry ,Mole fraction ,01 natural sciences ,chemistry.chemical_compound ,Methylpropane ,[CHIM]Chemical Sciences ,General Materials Science ,Physical and Theoretical Chemistry ,Solubility ,Imide ,Dissolution ,Alkyl ,chemistry.chemical_classification ,Isobutane ,Solvation ,021001 nanoscience & nanotechnology ,1-Alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,chemistry ,Ionic liquid ,Physical chemistry ,0210 nano-technology - Abstract
An experimental study of the solubility and of the thermodynamic properties of solvation, between temperatures (303 and 343) K and at pressures close to atmospheric, of 2-methylpropane (isobutane) in several ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion and on 1-alkyl-3-methylimidazolium cations, [C n C 1 Im][NTf 2 ], with alkyl side-chains varying from two to ten carbon atoms is presented. The isobutane solubility increases with increasing size of the alkyl side-chain of the cation in the ionic liquid and decreases with increasing temperature (as typical of an exothermal dissolution process). The mole fraction solubility of isobutane varies from 0.904 · 10 −2 in [C 2 C 1 Im][NTf 2 ] at T = 343 K to 1.002 · 10 −1 in [C 10 C 1 Im][NTf 2 ] at T = 303 K. The values measured in this work are compared to the behaviour of n-butane in the same ionic liquids published in a previous study (Costa Gomes et al. , 2012). Isobutane was found to be significantly less soluble than n-butane in all the ionic liquids. The differences found are interpreted in relation to the molecular structures obtained by molecular dynamics simulations for the solutions of n-butane and isobutane in the studied [C n C 1 Im][NTf 2 ] ionic liquids.
- Published
- 2015
36. Correction to 'Computationally Guided Discovery of Catalytic Cobalt-Decorated Metal–Organic Framework for Ethylene Dimerization'
- Author
-
Neil M. Schweitzer, Aaron B. League, Aaron W. Peters, Christopher J. Cramer, Laura Gagliardi, Joseph T. Hupp, Varinia Bernales, Rebecca K. Carlson, Zhanyong Li, and Omar K. Farha
- Subjects
Ethylene ,010405 organic chemistry ,Inorganic chemistry ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,General Energy ,chemistry ,Metal-organic framework ,Physical and Theoretical Chemistry ,Cobalt - Published
- 2017
37. Effect of unsaturation on the absorption of ethane and ethylene in imidazolium-based ionic liquids
- Author
-
Margarida F. Costa Gomes, Manas Mishra, Agilio A. H. Padua, Catherine C. Santini, Patricio Fuentealba, Varinia Bernales, Leila Moura, Institut de Chimie de Clermont-Ferrand (ICCF), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-SIGMA Clermont (SIGMA Clermont)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie, Catalyse, Polymères et Procédés, R 5265 (C2P2), Centre National de la Recherche Scientifique (CNRS)-École supérieure de Chimie Physique Electronique de Lyon (CPE)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École Supérieure de Chimie Physique Électronique de Lyon (CPE)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Bonnefoy, Stéphanie
- Subjects
Ethylene ,Inorganic chemistry ,Enthalpy ,Ionic Liquids ,02 engineering and technology ,Molecular Dynamics Simulation ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Polymer chemistry ,Materials Chemistry ,Side chain ,Physical and Theoretical Chemistry ,Solubility ,Alkyl ,chemistry.chemical_classification ,Degree of unsaturation ,Ethane ,Chemistry ,Viscosity ,Solvation ,Imidazoles ,Ethylenes ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,13. Climate action ,Ionic liquid ,0210 nano-technology - Abstract
International audience; The influence of the presence of imidazolium side chain unsaturation on the solubility of ethane and ethylene was studied in three ionic liquids: 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide--saturated alkyl side-chain in the cation; 1-methyl-3-(buten-3-yl)imidazolium bis(trifluorosulfonyl)imide--double bond in the side-chain of the cation; and 1-methyl-3-benzylimidazolium bis(trifluorosulfonyl)imide--benzyl group in the side-chain of the cation. The solubility of both gases decreases when the side-chain of the cations is functionalized with an unsaturated group. This can be explained by a less favorable enthalpy of solvation. The difference of solubility between ethane and ethylene can be explained from a balance of enthalpic and entropic factors: for the ionic liquid with the saturated alkyl side-chain and the benzyl-substituted side-chain, it is the favorable entropy of solvation that explains the larger ethylene solubility, whereas in the case of the saturated side-chain, it is the more favorable enthalpy of solvation. Molecular simulation allowed the identification of the mechanisms of solvation and the preferential solvation sites for each gas in the different ionic liquids. Simulations have shown that the entropy of solvation is more favorable when the presence of the gas weakens the cation-anion interactions or when the gas can be solvated near different sites of the ionic liquid.
- Published
- 2013
Catalog
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