Search

Electrophilic anions of type [B12 X11 ]- posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B12 X11 ]- with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N2 as σ-donor-π-acceptors. Temperature-dependent formation of [B12 X11 NG]- indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B12 X11 ]- and steric effects. The binding of CO and N2 to [B12 X11 ]- is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F)>(X=CN)>(X=Cl)>(X=Br)>(X=I), in contrast to the NG series. The bonding motifs of [B12 X11 CO]- and [B12 X11 N2 ]- were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N2 stretching frequencies νCO and νN2 , respectively. Observed shifts of νCO and νN2 are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B12 X11 ]- reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions.

The additive‐free tetrazine/enol ether click reaction was performed in ultra‐high vacuum (UHV) with an enol ether group covalently linked to a silicon surface: Dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate molecules were coupled to the enol ether group of a functionalized cyclooctyne which was adsorbed on the silicon (001) surface via the strained triple bond of cyclooctyne. The reaction was observed at a substrate temperature of 380 K by means of X‐ray photoelectron spectroscopy (XPS). A moderate energy barrier was deduced for this click reaction in vacuum by means of density functional theory based calculations, in good agreement with the experimental results. This UHV‐compatible click reaction thus opens a new, flexible route for synthesizing covalently bound organic architectures., Catalyst‐free coupling of a tetrazine derivative and an enol ether group, the latter being covalently attached on a Si(001) surface via cyclooctyne, has been observed in ultra‐high vacuum by X‐ray photoelectron spectroscopy. DFT calculations identified the associated reaction meachanism. This click chemistry scheme allows the synthesis of covalently bound molecular architectures on highly reactive surfaces in a UHV environment.

In this density functional theory study, the influence of the bonded dimer vacancy (DV) on the reactivity of the Si(001) surface is investigated. To this end, electronic and structural properties o...

The reaction of methyl enol ether functionalized cyclooctyne on the silicon (001) surface was investigated by means of X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Three different groups of final states were identified; all of them bind on Si(001) via the strained triple bond of cyclooctyne but they differ in the configuration of the methyl enol ether group. The majority of molecules adsorbs without additional reaction of the enol ether group; the relative contribution of this configuration to the total coverage depends on substrate temperature and coverage. Further configurations include enol ether groups which reacted on the silicon surface either via ether cleavage or enol ether groups which transformed on the surface into a carbonyl group., Binding via strained bond: Methyl enol ether functionalized cylooctyne is shown to adsorb on Si(001) preferentially via the strained triple bond of cyclooctyne. It can thus serve as an interface between the silicon surface and organic architectures which are coupled via the intact enol ether group. Side reactions include ether cleavage and the formation of an aldehyde group as observed by XPS and DFT.

The Sulfur (VI) Fluoride Exchange (SuFEx) reaction is an emerging scheme for connecting molecular building blocks. Due to its broad functional group tolerance and rather stable resulting linkage it is seeing rapid adoption in various fields of chemistry. Still, to date the reaction mechanism is poorly understood which hampers further development. Here, we show that the mechanism of the SuFEx reaction for the prototypical example of methanesulfonyl fluoride reacting with methylamine can be understood as an SN2-type reaction. By analyzing the reaction path with the help of density functional theory in vacuo and under consideration of solvent and co-reactant influence we identify the often used complementary base as crucial ingredient to lower the reaction barrier significantly by increasing the nucleophilicity of the primary amine. With the help of energy decomposition analysis (EDA) at the transition state structures we quantify the underlying stereo-electronic effects and propose new avenues for experimental exploration of the potential of SuFEx chemistry.

Corroles on metal surfaces show substantial reactivity and aromaticity-driven interfacial electron transfer of their transient σ/π-radicals. These effects are much more pronounced than for the clos...

The reaction of a methyl-substituted benzylazide on the silicon (001) surface was investigated by means of X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density f...

With the aim to mimic the yet unknown covalent deposition of metal chalcogenide clusters on transition metal dichalcogenide (TMDC) MoS2 or WS2 layers, and thereby explore the interaction between the two systems and potential consequences on physical properties of the TMDC material, we synthesized heterobimetallic model systems. The heterocubane-type cluster [(SnCl3)(WCp)3S4] (1), the organotin-sulfidomolybdate cluster [{(PhSn)3SnS6}{(MoCp)3S4}] (2), and the corresponding tungstate [(PhSn)3SnS6{(WCp)3S4}] (3) were obtained in ligand exchange reactions from [(PhSn)4S6] and [M(CO)3CpCl]. Indeed, the {M3S4} cages in 1-3 resemble a section of the respective TMDC monolayers, altogether representing minimal molecular model systems for the adsorption of organotin sulfide clusters on MoS2 or WS2. The interaction between the {(MCp)3S4} and {(PhSn)3SnS6} subunits is characterized by multicenter bonding, rendering the respective Sn atom as Sn(II), hence driving the clusters into a mixed-valence Sn(IV)/Sn(II) situation, and the M atoms as M(IV) upon an in situ redox process. The attachment is thus weaker than via regular covalent M-S bonds, but definitely stronger than via van der Waals interactions that have been characteristic for all known interactions of clusters on TMDC surfaces so far. Computational analyses of an extended model mimicking the electronic situation in the cluster prove the analogy to a covalent attachment on TMDCs.

A crucial factor determining charge transport in organic semiconductors is the electronic coupling between the molecular constituents, which is heavily influenced by the relative arrangement of the molecules. This renders quinacridone, with its multiple, structurally fundamentally different polymorphs and their diverse intermolecular interactions an ideal test case for analyzing the correlation between the electronic coupling in a specific configuration and the configuration's energetic stability. To provide an in-depth analysis of this correlation, starting from the $\alpha$-polymorph of quinacridone, we also construct a coplanar model crystal. This allows us to systematically compare the displacement-dependence of the electronic coupling with that of the total energy. In this way, we identify the combination of Pauli repulsion and orbital rehybridization as the driving force steering the system towards a structure in which the electronic coupling is minimal (especially for the valence band and at small displacements). The general nature of these observations is supported by equivalent trends for an analogous pentacene model system. This underlines that the design of high-performance materials cannot rely on the "natural" assembly of the $\pi$-conjugated backbones of organic semiconductors into their most stable configurations. Rather, it must include the incorporation of functional groups that steer crystal packing towards more favorable structures, where aiming for short-axis displacements or realizing comparably large long-axis displacements appear as strategies worthwhile exploring., Comment: This article has been removed by arXiv administrators because the submitter did not have the rights to agree to the license at the time of submission

Previous reports in the literature describe that the crystallization of hexaphenyl carbodiphosphorane (CDPPh) from a variety of solvents gives a “bent” geometry for the P–C–P moiety as the solid-st...

Disclosed herein is a visible light mediated cyclization of methyl (α-naphthyl) acrylates and heteroaromatic analogues yielding substituted acenaphthenes and azaacenaphthenes. This highly functional-group-tolerant transformation was put to the test in an enantioselective formal synthesis of delavatine A. Mechanistic details were elucidated by DFT-calculations revealing an unusual intramolecular H-transfer mediated by a primary amine. The generality of this transformation enables a novel synthetic strategy of five membered ring annulation at an advanced stage, allowing reliance upon naphthalene chemistry up to the point of acenaphthene construction.

The chemistry of organic adsorbates on surfaces is often discussed in terms of Pauli repulsion as limiting factor regarding the packing of molecules. Here we show that the attractive part of the van der Waals potential can be similarly decisive. For the semiconductor surface Si(001), an already covalently bonded molecule of cyclooctyne steers a second incoming molecule via dispersion interactions onto the neighbouring adsorption site. This helps in understanding the nonstatistical pattern formation for this surface–adsorbate system and hints toward an inclusion of dispersion attraction as another determining factor for surface adsorption.

Herein, we present a series of isomerically pure, peripherally alkyl substituted, soluble and low aggregating azaphthalocyanines as well as their new, smaller hybrid homologues, azasubphthalocyanines. The focus lies on the effect of the systematically increasing number of aza building blocks [-N[double bond, length as m-dash]] replacing the non-peripheral [-CH[double bond, length as m-dash]] units and their influence on the physical and photophysical properties of these chromophores. The absolute and relative HOMO-LUMO energies of azaphthalocyanines were analyzed using UV-Vis and CV and compared to the density functional theory calculations (B3LYP, TD-DFT). The lowering of the HOMO level is revealed as the determining factor for the trend in the adsorption energies by electronic structure analysis. Crystals of substituted subphthalocyanines, N2-Pc*H2 and N4-[Pc*Zn·H2O], were obtained out of DCM. For the synthesis of the valuable tetramethyltetralin phthalocyanine building block a new highly efficient synthesis involving a nearly quantitative CoII catalyzed aerobic autoxidation step is introduced replacing inefficient KMnO4/pyridine as the oxidant.

Surprising adsorption dynamics in terms of an either direct or pseudodirect pathway in contrast to common precursor-mediated surface reactions is shown for the title system by theoretical investigations. We present a computational protocol for the description of the adsorption dynamics in this complex system that is transferable to other large molecules. The system size prohibits the use of established accurate methods, and approximations have to be made and validated. Our approach combines potential energy surface scans, reaction path determination methods, statistical thermodynamics, and ab initio molecular dynamics simulations based on density functional theory (DFT). This leads to a conclusive picture of adsorption dynamics in the limits of DFT accuracy and shows how a thoughtful selection of methods can comprehensively describe the adsorption dynamics of an experimentally relevant system that might seem too complex for ab initio approaches at first glance.

Wir zeigen mit quantenchemischen Methoden, dass sich die Adsorption von Ether-Molekulen auf Si(001) im Ultrahochvakuum durch klassische Konzepte der organischen Molekulchemie verstehen lasst. Wie unsere detaillierte Analyse zeigt, spiegelt der zweistufige Mechanismus – 1) Ausbildung einer dativen Bindung zwischen dem Sauerstoffatom am Ether und einem Lewis-sauren Oberflachenatom, 2) nukleophiler Angriff eines nahegelegenen Lewis-basischen Oberflachenatoms – die saurekatalysierte Etherspaltung in Losung wider. Zudem ist die dative O-Si-Bindung die starkste ihrer Art und die Reaktivitat in Schritt 2 verlauft entgegen dem Bell-Evans-Polanyi-Prinzip. Mithilfe einer neuartigen Methode der Bindungsanalyse wird auserdem die Umverteilung von Elektronendichte wahrend des C-O-Bindungsbruchs visualisiert. Hierbei wird deutlich, dass der Mechanismus nukleophiler Substitutionen auf Halbleiteroberflachen identisch zu molekularen SN2-Reaktionen ist. Unsere Untersuchungen verdeutlichen, wie die Forschungsfelder der Oberflachenwissenschaften und Molekulchemie voneinander profitieren konnen und so unerwartete Einblicke ermoglichen.

Using computational chemistry, we show that the adsorption of ether molecules on Si(001) under ultra-high vacuum conditions can be understood with textbook organic chemistry. The two-step reaction mechanism of (1) dative bond formation between the ether oxygen and a Lewis acidic surface atom and (2) a nucleophilic attack of a nearby Lewis basic surface atom is analysed in detail and found to mirror the acid-catalysed ether cleavage in solution. The O-Si dative bond is found to be the strongest of its kind and reactivity from this state defies the Bell-Evans-Polanyi principle. Electron rearrangement during the C-O bond cleavage is visualized using a newly developed bonding analysis method, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular chemistry SN2 reactions. Our findings thus illustrate how the fields of surface science and molecular chemistry can mutually benefit and unexpected insight can be gained.

The performance of graphene-based (opto)electronic devices depends critically on the graphene/metal interface formed at the metal contacts. We show here that the interface properties may be controlled by topological defects, such as the pentagon–heptagon (5–7) pairs, because of their strongly enhanced bonding to the metal. To measure the bond energy and other key properties not accessible for the embedded defects, we use azulene as a molecular model for the 5–7 defect. Comparison to its isomer naphthalene, which represents the regular graphene structure, reveals that azulene interacts more strongly with a Pt(111) surface. Its adsorption energy, as measured by single-crystal adsorption calorimetry (SCAC), exceeds that of naphthalene by up to 116 kJ/mol (or up to 50%). Both isomers undergo hybridization of their frontier orbitals with metal states, as indicated by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with molecular orbital (MO) projection analysis through dispersion-corrected, periodic density functional theory (DFT) calculations. Based on the NEXAFS/DFT analysis, the stronger bond of the 5–7 system is attributed to the different energetic response of its unoccupied frontier orbitals to adsorption. Adsorption-induced bond-length changes show substantial topology-related differences between the isomers. Electron transfer occurs in both directions through donation/back-donation, resulting in the partial occupation (deoccupation) of formerly unoccupied (occupied) orbitals, as revealed by periodic energy decomposition analysis (pEDA) for extended systems. Our model study shows that the topology of the π-electron system strongly affects its bonding to a transition metal and thus can be utilized to tailor interface properties.\ud \ud

Organic/inorganic hybrid interfaces play a prominent role in organic (opto)electronics, heterogeneous catalysis, sensors, and other current fields of technology. The performance of the related devices and processes depends critically on the nature and strength of interfacial interaction. Here, we use the molecular isomers naphthalene (Nt) and azulene (Az) on the Ag(111) and Cu(111) surfaces as model systems that cover different bonding regimes from physisorption to chemisorption. Az also serves as a model for nonalternant molecular electronic materials and for topological 5–7 defects in graphene. The interaction energies are determined from the quantitative analysis of temperature-programmed desorption data. On both surfaces, Az binds more strongly than Nt, with zero-coverage desorption energies (in kJ/mol) of 120 for Az/Ag and 179 for Az/Cu, compared to 103 for Nt/Ag and 114 for Nt/Cu. The integrated experimental energies are compared with adsorption energies from density-functional theory (DFT) calculations, which include van der Waals contributions using four different correction schemes for the PBE functional: (1) the DFT-D3 scheme with Becke–Johnson damping, (2) the vdWsurf correction based on DFT-TS, (3) a many-body dispersion correction scheme, and (4) the D3surf scheme. Differences in the performance of these methods are discussed. Periodic energy decomposition analysis reveals details of the surface chemical bond and confirms that Az/Cu forms a chemisorptive bond, while the other systems are physisorbed. The variation of the adsorbate–substrate interaction with the topology of the π-electron system and the type of surface can be employed to modify the interface properties in graphene-based and organic electronic devices.

Phthalocyanines possess unique optical and electronic properties and thus are widely used in (opto)electronic devices, coatings, photodynamic therapy, etc. Extension of their π-electron systems could produce molecular materials with red-shifted absorption for a broader range of applications. However, access to expanded phthalocyanine analogues with more than four isoindoline units is challenging due to the limited synthetic possibilities. Here, we report the controlled on-surface synthesis of a gadolinium-supernaphthalocyanine macrocycle and its open-chain counterpart poly(benzodiiminoisoindoline) on a silver surface from a naphthalene dicarbonitrile precursor. Their formation is controlled by the on-surface high-dilution principle and steered by different metal templates, i.e., gadolinium atoms and the bare silver surface, which also act as oligomerization catalysts. By using scanning tunneling microscopy, photoemission spectroscopy, and density functional theory calculations, the chemical structures along with the mechanical and electronic properties of these phthalocyanine analogues with extended π-conjugation are investigated in detail., Extending the π‐conjugation of phthalocyanine dyes, while synthetically challenging, has the potential to produce desirable new molecular materials. Here, the authors use a templated on‐surface approach to synthesize several extended phthalocyanine derivatives from the same building block, including a lanthanide superphthalocyanine and an open‐chain polycyanine.

(Me2C[double bond, length as m-dash]NMe2)Bi2I7 represents a new layered organic-inorganic iodido bismuthate. It displays an unprecedented anion topology, a low band gap and good stability. Advanced electronic structure analysis finds the II interactions to be decisive for the compound's structural and electronic properties.

We report the use of bioorthogonal reactions as an original strategy in photodynamic therapy to achieve conditional phototoxicity and specific subcellular localization simultaneously. Our novel halogenated BODIPY-tetrazine probes only become efficient photosensitizers (ΦΔ ≈0.50) through an intracellular inverse-electron-demand Diels-Alder reaction with a suitable dienophile. Ab initio computations reveal an activation-dependent change in decay channels that controls 1 O2 generation. Our bioorthogonal approach also enables spatial control. As a proof-of-concept, we demonstrate the feasibility of the selective activation of our dormant photosensitizer in cellular nuclei, causing cancer cell death upon irradiation. Thus, our dual biorthogonal, activatable photosensitizers open new venues to combat current limitations of photodynamic therapy.

The adsorption characteristics of a promising system for hybrid organic-inorganic interfaces, cyclooctyne on Si(001), is analyzed using density functional theory. The chemisorbed 'on-top' configuration, where a cycloadduct is formed between the ring triple bond and a surface dimer, is shown to be most stable. Less stable are 'bridge' and 'sublayer' modes featuring two molecule-surface bonds and the 'pedestal' mode with four bonds. Investigations with our recently proposed periodic energy decomposition analysis (pEDA) reveal that the four-bond configuration is destabilized by large deformation energies needed within molecule and surface as well as rather weak molecule-surface bonds. Dispersion interactions show significant influence on energy and structure of the configurations leading to an increased bending of the rather flexible molecules. Thus, features found in previous scanning tunneling microscopy experiments are conclusively explained with bent 'on-top' configurations and the 'pedestal' mode can be ruled out. A comparison to acetylene shows that the ring structure and the resulting strain of cyclooctyne are responsible for an increased reactivity of the larger adsorbate due to a pre-forming of the ring triple bond for surface bonding. In contrast, ring strain leads only to negligible electronic effects on the adsorbate-surface bonds. The computations highlight the need for in-depth theoretical analysis to understand adsorption characteristics of large, flexible molecules.

We report differences in adsorption and reaction energetics for ethylene on Si(001) with respect to different dangling bond configurations induced by hydrogen precoverage as obtained via density functional theory calculations. This can help to understand the influence of surface defects and precoverage on the reactivity of organic molecules on semiconductor surfaces in general. Our results show that the reactivity on surface dimers fully enclosed by hydrogen covered atoms is essentially unchanged compared to the clean surface. This is confirmed by our scanning tunnelling microscopy measurements. On the contrary, adsorption sites with partially covered surface dimers show a drastic increase in reactivity. This is due to a lowering of the reaction barrier by more than fifty percent compared to the clean surface, which is in line with previous experiments. Adsorption on dimers enclosed by molecule (ethylene) covered surface atoms is reported to have a highly decreased reactivity, a result of destabilization of the intermediate state due to steric repulsion, as quantified with the periodic energy decomposition analysis (pEDA). Furthermore, an approach for the calculation of Gibbs energies of adsorption based on statistical thermodynamics considerations is applied to the system. The results show that the loss in molecular entropy leads to a significant destabilization of adsorption states.

Intermediate states to covalent attachment of molecules on surfaces, so called precursors, are usually considered to be physisorbed and mobile. We show that this view should be reconsidered and provide evidence for a chemisorbed precursor for ethylene on Si(001). The character of the molecule-surface bond as a π complex is determined and quantified using our recently developed method for energy and charge analysis in extended systems. In contrast to previous assumptions, the precursor should thus be immobile, which is underlined by computation of high diffusion energy barriers. This has important implications for understanding and modelling of adsorption kinetics. Our analysis highlights that taking the viewpoint of molecular chemistry helps uncover important aspects in the adsorption process on surfaces. Previous experimental results that appear to be in contrast to our model are examined and reinterpreted.

Wir prasentieren Rechnungen der Kohasionsenergie von Argon in der kubisch und hexagonal dichtesten Kugelpackung mit einer noch nie zuvor erreichten Genauigkeit im Bereich von 5 J mol−1 (dies entspricht 0.05 % der gesamten Kohasionsenergie). Dieselbe relative Genauigkeit im Vergleich zu experimentellen Daten wurde auch fur die Gitterkonstante des flachenzentrierten Gitters mit einer absoluten Abweichung von ungefahr 0.003 A erreicht. Die hohe Genauigkeit wurde durch die Verwendung von wellenfunktionsbasierten Methoden im Rahmen einer Mehrkorperentwicklung der Wechselwirkungsenergie ermoglicht. Statische Beitrage der Zwei-, Drei- und Vierkorperfragmente des Kristalls, die jeweils mit einer Genauigkeit von unter 1 J mol−1 berechnet wurden, wurden durch harmonische und anharmonische Nullpunktschwingungskorrekturen erganzt. Fur Edelgas-Festkorper erreicht die Computerchemie hiermit experimentelle Genauigkeit oder ubertrifft diese sogar.

We combine density functional theory calculations and scanning tunneling microscopy investigations to identify the relevant chemical species and reactions in the nucleation phase of chemical vapor deposition. tert-Butylphosphine (TBP) was deposited on a silicon substrate under conditions typical for surface functionalization and growth of semiconductor materials. On the activated hydrogen-covered surface H/Si(001) it forms a strong covalent P-Si bond without loss of the tert-butyl group. Calculations show that site preference for multiple adsorption of TBP is influenced by steric repulsion of the adsorbate's bulky substituent. STM imaging furthermore revealed an anisotropic distribution of TBP with a preference for adsorption perpendicular to the surface dimer rows. The adsorption patterns found can be understood by a mechanism invoking stabilization of surface hydrogen vacancies through electron donation by an adsorbate. The now improved understanding of nucleation in thin-film growth may help to optimize molecular precursors and experimental conditions and will ultimately lead to higher quality materials.

The effect of several Lewis acids on the CBS catalyst (named after Corey, Bakshi and Shibata) was investigated in this study. While (2) H NMR spectroscopic measurements served as gauge for the activation capability of the Lewis acids, in situ FT-IR spectroscopy was employed to assess the catalytic activity of the Lewis acid oxazaborolidine complexes. A correlation was found between the Δδ((2) H) values and rate constants kDA , which indicates a direct translation of Lewis acidity into reactivity of the Lewis acid-CBS complexes. Unexpectedly, a significant deviation was found for SnCl4 as Lewis acid. The SnCl4 -CBS adduct was much more reactive than the Δδ((2) H) values predicted and gave similar reaction rates to those observed for the prominent AlBr3 -CBS adduct. To rationalize these results, quantum mechanical calculations were performed. The frontier molecular orbital approach was applied and a good correlation between the LUMO energies of the Lewis acid-CBS-naphthoquinone adducts and kDA could be found. For the SnCl4 -CBS-naphthoquinone adduct an unusual distortion was observed leading to an enhanced Lewis acidity. Energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) calculations revealed the relevant interactions and activation mode of SnCl4 as Lewis acid in Diels-Alder reactions.

The reaction of hexaphenyl-carbodiphosphorane C(PPh3)2 (CDP, 1) with BF3·OEt2 provides the corresponding difluoroborenium cation [CDP–BF2]+ (2+) through fluoride abstraction. Advanced NMR spectroscopy methods, including 19F,31P HMQC; 31P,13C HMQC; 19F,1H HOESY; 19F NOESY; 31P,13C INEPT; and 1H, 31P, 19F, and 11B diffusion NMR measurements, were performed, and they revealed strong ion pairing of 2+ with the [BF4]– counterion in chloroform solution. Structural and computational studies showed strong donor–acceptor interactions, in which the σ and π lone pairs of electrons of C(PPh3)2 donate into the vacant orbitals of the [BF2]+ fragment. The C–B bond shows the highest interaction energy of 242.9 kcal mol–1 found for the corresponding carbodiphosphorane adducts.

Depending on the temperature, the twofold deprotonation of 1,1′-methylenebis(3-methylimidazole-2-thione) (1) and the subsequent reaction with 2 equiv. of trimethylsilyl chloride (TMSCl) gives two different bis-TMS-functionalized isomers, namely, 1,1′-methylenebis(3-methyl-4-trimethylsilylimidazole-2-thione) (2) and 1,1′-methylenebis(3-methyl-5-trimethylsilylimidazole-2-thione) (3). The cyclic dimethylsilyl-bridged derivative 1,1′-methylene-5,5′-dimethylsilylenebis(3-methylimidazole-2-thione) (4) can also be obtained, corroborating the 5/5′ addition under certain conditions. All compounds have been examined by multinuclear 1D and 2D NMR experiments (1–4) together with single-crystal X-ray diffraction (3 and 4). Additionally, the dilithiated species 5 was synthesized by reacting 1 with 2 equiv. of nBuLi at ambient temperature in solution (THF). 1H and 7Li pulsed field-gradient spin-echo (PGSE) NMR, 7Li–1H heteronuclear Overhauser spectroscopy (HOESY), gradient heteronuclear multiple quantum correlation (gHMQC) and gradient heteronuclear multiple bond correlation (gHMBC) experiments showed that 5 exists as a monomeric contact ion pair (CIP) in THF solution. On the contrary, the X-ray diffraction analysis of 5 revealed a polymeric chain, which can be described as [{5(thf)2}2]∞. Quantum chemical DFT and MP2 calculations were also conducted to determine the energies required for the deprotonation of 1. These results explain the regioselective deprotonation of 1 by CIP formation depending on the temperature and fully support the results of the synthetic and spectroscopic experiments.

III/V semiconductors containing small amounts of nitrogen (N; dilute nitrides) are discussed in the context of different solar cell and laser applications. The efficiency of these devices is negatively affected by carbon (C) incorporation, which comes either from the direct C–N bond in the N precursor unsymmetrical 1,1-dimethylhydrazine (UDMHy) used conventionally or from the alkyl groups of the conventional precursors for gallium (Ga), indium and arsenic (As) containing carbon. This C is incorporated together with the N due to the strength of the C–N bond. A further important issue in dilute nitride growth is the very low N incorporation efficiency in the crystal from UDMHy, which can be as little as 1% of the N supplied in the gas phase. Therefore, new metal organic chemicals have to be synthesized and their growth characteristics and suitability for dilute nitride growth have to be explored. This work presents the chemical di-tertiary-butyl-arsano-amine (DTBAA), which was synthesized, purified and tested as an N precursor for metal organic vapor phase epitaxy (MOVPE). Computational investigations show β-hydrogen and isobutane elimination to be the main reaction channel in the gas phase with high reaction barriers and absence of small fragments containing C as products. The loss of N via N2, as in UDMHy, can be excluded for unimolecular reactions of DTBAA. The Ga(NAs)/GaAs heterostructures were grown by MOVPE as initial test material and a systematic N incorporation study is presented in this paper. It is shown that high quality Ga(NAs) can be grown using DTBAA. The N incorporation was confirmed by high resolution X-ray diffraction and photoluminescence studies. All samples grown exhibit as grown room temperature photoluminescence and smooth surface morphologies. Furthermore, DTBAA shows extremely high N incorporation efficiency, which makes this molecule a very promising candidate for further research into dilute nitride material growth.

Interfaces between polycyclic π-electron systems and metals play prominent roles in organic or graphene-based (opto)electronic devices, in which performance-related parameters depend critically on the properties of metal/semiconductor contacts. Here, we explore how the topology of the π-electron system influences the bonding and the electronic properties of the interface. We use azulene as a model for nonalternant pentagon–heptagon (5–7) ring pairs and compare it to its isomer naphthalene, which represents the alternant 6–6 ring pair. Their coverage-dependent interaction with Ag(111) and Cu(111) surfaces was studied with the normal-incidence X-ray standing wave (NIXSW) technique, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, UV and X-ray photoelectron spectroscopies (UPS and XPS), and density functional theory (DFT). Coverage-dependent adsorption heights and spectroscopic data reveal that azulene forms shorter interfacial bonds than naphthalene and engages in stronger electronic interactions with both surfaces. These differences are more pronounced on Cu. Increasing coverages lead to larger adsorption heights, indicating bond weakening by intermolecular repulsion. The extensive DFT calculations include dispersive interactions using (1) the DFT-D3 scheme, (2) the vdWsurf correction based on DFT-TS, (3) a many-body dispersion (MBD) correction scheme, and (4) the D3surf scheme. All methods predict the adsorption heights reasonably well with an average error below 0.1 A. The stronger bond of azulene is attributed to its nonalternant topology, which results in a reduced highest occupied molecular orbital (HOMO)–lowest occupied molecular orbital (LUMO) gap and brings the LUMO energetically close to the Fermi energy of the metal, causing stronger hybridization with electronic states of the metal surfaces.

The chemoselective bonding of a bifunctional organic molecule on a semiconductor surface is analyzed with density functional theory (DFT). Periodic energy decomposition analysis is used to reveal the bonding characteristics of different adsorption modes and transition states for 5-ethoxymethyl-5-methylcyclooctyne on Si(001). This system has previously been experimentally proven to be a prototype model system for inorganic–organic hybrid interfaces. The molecule thereby poses challenges for a theoretical description of conformational flexibility and competitive adsorption behavior of the two functional groups. We find that adsorption via the strained triple bond is preferred over the ether group, thus confirming previous experiments. Bonding analysis in combination with static DFT as well as ab initio molecular dynamics methods thereby reveals the determining factors for this chemoselectivity and shows that the functional groups barely influence each other in their surface adsorption.

Using density functional theory (DFT) methods, we analyze the adsorption of acetylene and ethylene on the Si(001) surface in an unusual bond insertion mode. The insertion takes place at a saturated tetravalent silicon atom and the insight gained can thus be transferred to other saturated silicon compounds in molecular and surface chemistry. Molecular orbital analysis reveals that the distorted and symmetry-reduced coordination of the silicon atoms involved due to surface reconstruction raises the electrophilicity and, additionally, makes certain σ bond orbitals more accessible. The affinity towards bond insertion is, therefore, caused by the structural constraints of the surface. Additionally, periodic energy decomposition analysis (pEDA) is used to explain why the bond insertion structure is much more stable for acetylene than for ethylene. The increased acceptor abilities of acetylene due to the presence of two π*-orbitals (instead of one π*-orbital and a set of σ*(C–H) orbitals for ethylene), as well as the lower number of hydrogen atoms, which leads to reduced Pauli repulsion with the surface, are identified as the main causes. While our findings imply that this structure might be an intermediate in the adsorption of acetylene on Si(001), the predicted product distributions are in contradiction to the experimental findings. This is critically discussed and suggestions to resolve this issue are given.

A method for accessing the formally 14 VE iridium(III) hydride fragment {Ir(IBioxMe4)2(H)2}+ (2), containing the conformationally rigid NHC ligand IBioxMe4, is reported. Hydrogenation of trans-[Ir(IBioxMe4)2(COE)Cl] (1) in the presence of excess Na[BArF4] leads to the formation of dimeric [{Ir(IBioxMe4)2(H)2}2Cl][BArF4] (3), which is structurally fluxional in solution and acts as a reservoir of monomeric 2 in the presence of excess halogen ion abstractor. Stable dihydride complexes trans-[Ir(IBioxMe4)2(2,2′-bipyridine)(H)2][BArF4] (4) and [Ir(IBioxMe4)3(H)2][BArF4] (5) were subsequently isolated through in situ trapping of 2 using 2,2′-bipyridine and IBioxMe4, respectively, and fully characterized. Using mixtures of 3 and Na[BArF4] as a latent source of 2, the reactive monomeric fragment’s reactivity was explored with excess ethylene and cyclooctene, and trans-[Ir(IBioxMe4)2(C2H4)2][BArF4] (6) and cis-[Ir(IBioxMe4)2(COD)][BArF4] (7) were isolated, respectively, through sacrificial hydrogenation of the alkenes. Complex 6 is notable for the adoption of a very unusual orthogonal arrangement of the trans-ethylene ligands in the solid state, which has been analyzed computationally using energy and charge decomposition (EDA-NOCV). The formation of 7 via transfer dehydrogenation of COE highlights the ability to partner IBioxMe4 with reactive metal centers capable of C–H bond activation, without intramolecular activation. Reaction of 7 with CO slowly formed trans-[Ir(IBioxMe4)2(CO)2][BArF4] (8), but the equivalent reaction with bis-ethylene 6 was an order of magnitude faster, quantifying the strong coordination of COD in 7.

Two new, isostructural members of the title material class, [PPh4]4[Cu2Bi2I12] (1) and [PPh4]4[Ag2Bi2I12] (2), have been prepared via a facile solution route. The crystal structure of both compounds features a tetranuclear [M2Bi2I12]4– (M = Cu, Ag) anion that displays an unprecedented face-sharing mode of connection between BiI6 octahedra and MI4 tetrahedra, enabling close Bi···M contacts. The two compounds allow for a direct experimental and quantum chemical investigation of the influence of group 11 metal cations on the optical and electronic properties of ternary iodido bismuthate anions, indicating that Cu+ is a better electronic match than Ag+, resulting in a significantly lower optical band gap of the copper compound.

Alkylboranes, such as trimethylboron (TMB) and triethylboron (TEB), are promising alternative precursors in low temperature chemical vapor deposition (CVD) of boron-containing thin films. In this study, CVD growth of B-C films using TMB and quantum-chemical calculations to elucidate a gas phase chemical mechanism were undertaken. Dense, amorphous, boron-rich (B/C 1.5-3) films were deposited at 1000 degrees C in both dihydrogen and argon ambients, while films with crystalline B4C and B25C inclusions were deposited at 1100 degrees C in dihydrogen. A script-based automatization scheme was implemented for the quantum-chemical computations to enable time efficient screening of thousands of possible gas phase CVD reactions. The quantum-chemical calculations suggest TMB is mainly decomposed by an unimolecular alpha-H elimination of methane, which is complemented by dihydrogen-assisted elimination of methane in dihydrogen. Funding Agencies|European Spallation Source ERIC; Knut and Alice Wallenberg Foundation; German Science Foundation [GRK 1782]; Swedish Foundation for Strategic Research (SSF) [IS14-0027]; COST Action [MP1402]; COST (European Cooperation in Science and Technology); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

The cohesive energies of argon in its cubic and hexagonal closed packed structures are computed with an unprecedented accuracy of about 5 J mol(-1) (corresponding to 0.05 % of the total cohesive energy). The same relative accuracy with respect to experimental data is also found for the face-centered cubic lattice constant deviating by ca. 0.003 Å. This level of accuracy was enabled by using high-level theoretical, wave-function-based methods within a many-body decomposition of the interaction energy. Static contributions of two-, three-, and four-body fragments of the crystal are all individually converged to sub-J mol(-1) accuracy and complemented by harmonic and anharmonic vibrational corrections. Computational chemistry is thus achieving or even surpassing experimental accuracy for the solid-state rare gases.

We present computational results on dynamics and properties of semiconductor materials and interfaces. The adsorption of cyclooctyne on silicon can be shown to proceed barrierless into an on-top structure. Comparing different interfaces of the GaP/Si system, a preference for mixed interfaces (i.e. not purely Si/Ga or Si/P) can be found and understood in terms of the electrostatic potential across the interface and chemical bonding specifics. In further work, the electronic structure of mixed III/V semiconductors will be studied in the way described here for GaAs and used for the prediction of optical properties.

We introduce a simple but computationally very efficient harmonic force field, which works for all fullerene structures and includes bond stretching, bending, and torsional motions as implemented into our open-source code Fullerene. This gives accurate geometries and reasonably accurate vibrational frequencies with root mean square deviations of up to 0.05 A for bond distances and 45.5 cm(-1) for vibrational frequencies compared with more elaborate density functional calculations. The structures obtained were used for density functional calculations of Goldberg-Coxeter fullerenes up to C980. This gives a rather large range of fullerenes making it possible to extrapolate to the graphene limit. Periodic boundary condition calculations using density functional theory (DFT) within the projector augmented wave method gave an energy difference between -8.6 and -8.8 kcal/mol at various levels of DFT for the reaction C60 →graphene (per carbon atom) in excellent agreement with the linear extrapolation to the graphene limit (-8.6 kcal/mol at the Perdew-Burke-Ernzerhof level of theory).