Ralf Tonner | Philipps Universität Marburg (original) (raw)
Papers by Ralf Tonner
Inorganic Chemistry, 2015
The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (e... more The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (element E = N-Bi) were investigated and compared to the group 13 example of GaH2(t-C4H9). With the aid of extensive density functional theory based analysis of atomic and electronic structures at the transition state, we can derive three distinct reaction classes. The gallium compound follows the well-known β-hydride route with participation of an empty p orbital at the metal in a concerted, synchronous fashion, exhibiting a low barrier. For compounds with group 15 elements, we find highly nonsynchronous reactions with high reaction barriers. In the case of nitrogen, a proton-like H atom is transferred via attack of the nitrogen nonbonding electron pair. For the heavier homologues (P-Bi), E-Cα bond breaking occurs first and the H atom does not carry charge at the transition state. The reaction barrier in group 15 homologues is thus determined by the E-Cα bond strength down the group. The results enable a rationale for ligand design for precursors involved in chemical vapor-phase deposition processes because a good ligand needs to stabilize the positive charge at Cα.
The transition from postdoc to Principal Investigator (PI) is a crucial one, and certainly unique... more The transition from postdoc to Principal Investigator (PI) is a crucial one, and certainly unique among the many transitions (high school student-college student, college studentgrad student, grad student-postdoc) in an academic career. We can thus not build on a vast reservoir of personal experiences during the beginning of this phase. Furthermore, although many major universities offer professional development centers, there is no overabundance of courses and seminars you can take to prepare for this step. In the best case, you have a good mentor, but also their advice is (almost by necessity) largely limited to their own experience. In order to provide some hints as to what points you might consider yourself and as a guide for professional development offices, we decided to compile a list of the things that caught us off guard to a certain extent when we started our careers as independent PIs. Naturally, such a list is heavily skewed towards our experience and by no means representative, but we feel that these are recurring themes and sometimes easily avoided with a bit of preparation. Even if some of the points we make are rather obvious, it might be comforting for other young PIs to know that they are not the only ones encountering certain problems. We have structured the points by grouping them into four categories: (i) The challenges of time management; (ii) points regarding personal development; (iii) dealing with students and co-workers and (iv) colleagues and the scientific community. Finally, we compiled some potential solutions and strategies that have been helpful for us and provide our ideas about improving some of the points raised.
Theoretical Chemistry Accounts, 2010
The possible existence of the gas phase cis-and trans-maleate, i.e. completely deprotonated malei... more The possible existence of the gas phase cis-and trans-maleate, i.e. completely deprotonated maleic acid (O 2 C-CH=CH-CO 2 ) 2-, is investigated by density functional (B3LYP) and ab-initio quantum chemical methods (MP2, CCSD(T)) using large basis sets. The calculations reveal that only the trans-isomer is Coulomb stable with respect to electron loss. The results are compared to other previously investigated dicarboxylate dianions of the general form -O 2 C-R-CO 2 with R = C 2 , C 2 X 2 , C 2 X 4 , and C 6 X 4 (X = H, F). Fluorine substitution on the carbon framework helps to stabilize these doubly charged systems, and we predict that all of the aromatic fluorine substituted dicarboxylate dianions are Coulomb stable in the gas phase. Only the highest levels of theory reveal the slight stabilization of both the succinate dianion and the orthoisomer of the phthalic acid dianion in unprecedented agreement with experiments.
ChemPhysChem, 2010
The optimal adsorption modes for the amino acids glycine and proline on the ideal TiO(2)(110) sur... more The optimal adsorption modes for the amino acids glycine and proline on the ideal TiO(2)(110) surface are investigated by using density functional theory (PBE) applying periodic boundary conditions. Binding modes with anionic acid moieties bridging two titanium atoms after transferring a proton to the surface are the most stable configurations for both molecules investigated-similar to previous results for carboxylic acids. In contrast to the latter compounds, amino acids can form hydrogen bonds via the amino group towards the surface-bound proton; this provides an additional stabilisation of 15-20 kJ mol(-1). Zwitterionic binding modes are less stable (by 10-20 kJ mol(-1)) and are less important for proline. Neutral modes are energetically even less favourable. Calculations of vibrational frequencies and core-level shifts complement the adsorption study and provide guidance for future experimental investigations. Control of the computational parameters is crucial for the derivation of accurate results. The layout and thickness of the slab model used are also shown to be decisive factors. Calculations with a different GGA-functional (PW91) provide very similar relative energies, although the absolute energies change by about 20 kJ mol(-1). Results derived with the hybrid functional PBE0 show an even greater stabilisation of the anionic binding modes with respect to the zwitterionic modes. A previously observed discrepancy between experimental and theoretical results for glycine could be solved, although the experimentally proposed free rotation of the C-C bond could not be reproduced.
In an effort to understand the chemical factors that stabilize dianions, experimental and theoret... more In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O2C–CH(OH)–CH(OH)–CO2)2– → (O2C–CH(OH)–CH(OH))•– + CO2 + e– explaining the observed gas-phase instability of this dianion. Further theoretical data
The Journal of Chemical Physics, 2015
The development and first applications of a new periodic energy decomposition analysis (pEDA) sch... more The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the binding energy between two fragments (e.g. the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic and dispersion interaction, Pauli repulsion and orbital relaxation energies. The pEDA presented here for an AO-based implementation can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy and k-space sampling. Four typical bonding scenarios for surface adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H2 on M(001), M = Pd, Cu) and semiconducting (CO and C2H2 on Si(001)c(4x2)) substrates. These examples cover the regimes of metallic, semiconducting and insulating substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence, that the pEDA will be a powerful tool for the analysis of surfaceadsorbate binding in the future, enabling the transfer of concepts like ionic and covalent binding, donor-acceptor interaction, steric repulsion and others to extended systems.
High Performance Computing in Science and Engineering '05, 2006
... Acc. 99 (1998), 391 S [17] EJ Baerends; JA Autschbach; A. Berces; C. Bo; PM Boerrigter; L. Ca... more ... Acc. 99 (1998), 391 S [17] EJ Baerends; JA Autschbach; A. Berces; C. Bo; PM Boerrigter; L. Cavallo; DP Chong; L. Deng; RM Dickson; DE Ellis; L. Fan; TH Fischer; C. Fonseca Guerra; SJA van Gisbergen; JA ... 136 (1987), 52 S [37] Demaison, J.; Hegelund, F.; Burger, H.: In: J. Mol ...
Chemical Science, 2011
ABSTRACT It is shown that vanadium-iminato ligands are more efficient than imidazolidin-2-iminato... more ABSTRACT It is shown that vanadium-iminato ligands are more efficient than imidazolidin-2-iminato substituents to delocalize the spin density from a phosphorus nucleus. However, the latter is stabilizing enough to allow for the isolation and characterization in the liquid and solid states of a neutral phosphinyl radical.
Wiley Interdisciplinary Reviews-Computational Molecular Science, 2011
Physical chemistry chemical physics : PCCP, 2014
The gas phase decomposition reactions of precursor molecules relevant for metal-organic vapour ph... more The gas phase decomposition reactions of precursor molecules relevant for metal-organic vapour phase epitaxy (MOVPE) of semiconductor thin films are investigated by computational methods on the density-functional level as well as on the ab initio (MP2, CCSD(T)) level. A comprehensive reaction catalogue of uni- and bimolecular reactions is presented for triethylgallium (TEG) as well as for tert-butylphosphine (TBP) containing thermodynamic data together with transition state energies. From these energies it can be concluded that TEG is decomposed in the gas phase under MOVPE conditions (T = 400-675 °C, p = 0.05 atm) to GaH3via a series of β-hydride elimination reactions. For elevated temperatures, further decomposition to GaH is thermodynamically accessible. In the case of TBP, the original precursor molecule will be most abundant since all reaction channels exhibit either large barriers or unfavorable thermodynamics. Dispersion-corrected density functional calculations (PBE-D3) provide an accurate description of the reactions investigated in comparison to high level CCSD(T) calculations serving as benchmark values.
Organometallics, 2011
The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents... more The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions.
Chemical Society reviews, Jan 21, 2014
Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the ... more Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the singlet (1)D state behave as bidentate Lewis acids that strongly bind two σ donor ligands L in the donor-acceptor complexes L→E←L. Tetrylones EL2 are divalent E(0) compounds which possess two lone pairs at E. The unique electronic structure of tetrylones (carbones, silylones, germylones, stannylones, plumbylones) clearly distinguishes them from tetrylenes ER2 (carbenes, silylenes, germylenes, stannylenes, plumbylenes) which have electron-sharing bonds R-E-R and only one lone pair at atom E. The different electronic structures of tetrylones and tetrylenes are revealed by charge- and energy decomposition analyses and they become obvious experimentally by a distinctively different chemical reactivity. The unusual structures and chemical behaviour of tetrylones EL2 can be understood in terms of the donor-acceptor interactions L→E←L. Tetrylones are potential donor ligands in main group compou...
Zeitschrift für anorganische und allgemeine Chemie, 2007
The Journal of Physical Chemistry C, 2012
ABSTRACT Vibrational properties of highly ordered crystalline perfluoropentacene (PFP) films epit... more ABSTRACT Vibrational properties of highly ordered crystalline perfluoropentacene (PFP) films epitaxially grown on KCl(100) and NaF(100) substrates have been studied by means of transmission infrared spectroscopy and density functional theory. The different molecular orientations adopted by PFP on both substrates (standing vs lying) and their epitaxial ordering enable precise polarization-resolved measurements along individual crystallographic directions and thus allow an unambiguous experimental determination of the polarization of the IR modes. Computations of the vibrational spectra beyond the single-molecule approximation were employed at the periodic dispersion-corrected density functional level (PBE-D2PBC) and compared with nonperiodic calculations (PBE-D2/def2-TZVPP). Thereby, a detailed mode assignment based on vibrational energies and polarization information was attained. A microscopic explanation for the experimentally observed Davydov splitting of some modes and the IR inactivity of others was derived based on the mutual coupling of the dynamical dipole moments of the two molecules within the unit cell. Experimentally observed modes not covered by our theoretical analysis have been identified as combination bands of IR-active modes coupled to totally symmetric modes of similar displacement patterns. These findings have important implications for future studies on structure and charge transport in organic semiconductors and the validation of theoretical approaches for the modeling of vibrational spectra.
The Journal of Physical Chemistry A, 2012
In an effort to understand the chemical factors that stabilize dianions, experimental and theoret... more In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O 2 C− CH(OH)−CH(OH)−CO 2 ) 2− → (O 2 C−CH(OH)−CH-(OH)) •− + CO 2 + e − explaining the observed gas-phase instability of this dianion. Further theoretical data were collected for the bare dianion, this molecule complexed to water, sodium, and a proton, in both the meso and L forms as well as for the uncomplexed radical anion and neutral diradical. The calculations suggest that the L-tartrate dianion is more thermodynamically stable than the dianion of the meso stereoisomer and that either dianion can be further stabilized by association with a separate species that can help to balance the charge of the molecular complex. Mass spectrometry was then used to measure the energy needed to initiate collisionally induced dissociation of the racemic tartrate dianion and for the proton and sodium adducts of both the racemic and meso form of this molecule. Infrared action spectra of the dianion stereoisomers complexed with sodium were also acquired to determine the influence of the metal ion on the vibrations of the dianions and validate the computationally predicted structures. These experimental data support the theoretical conclusions and highlight the instability of the bare tartrate dianion. From the experimental work, it could also be concluded that the pathway leading to dissociation is under kinetic control because the sodium adduct of the racemic stereoisomer dissociated at lower collisional energy, although it was calculated to be more stable, and that decomposition proceeded via C−C bond dissociation as computationally predicted. Taken together, these data provide insight into the gas-phase stability of the tartrate dianion and highlight the role of adducts in stabilizing this species. Figure 1. Stereoisomers of tartaric acid. Article pubs.acs.org/JPCA
Pure and Applied Chemistry, 2000
Physical Review B, 2006
The many-body expansion V int = ͚ iϽj V ͑2͒ ͑r ij ͒ + ͚ iϽjϽk V ͑3͒ ͑r ij , r ik , r jk ͒ +¯, in ... more The many-body expansion V int = ͚ iϽj V ͑2͒ ͑r ij ͒ + ͚ iϽjϽk V ͑3͒ ͑r ij , r ik , r jk ͒ +¯, in terms of interaction potentials between rare-gas atoms converges fast at distances r Ͼ r HS , with r HS being the hard-sphere radius at the start of the repulsive wall of the interaction potential. Hence, for the solid state where the minimum distance is always above r HS , a reasonable accuracy is already obtained for the lattice parameters and cohesive energies of the rare-gas elements using precise two-body terms. All tested two-body potentials show a preference of the hcp over the fcc structure. We demonstrate that this is always the case for the Lennard-Jones potential. We extend the Lennard-Jones potential to obtain analytical expressions for the lattice parameters, cohesive energy, and bulk modulus using the solid-state parameters of Lennard-Jones and Ingham ͓Proc. R. Soc. London, Ser. A 107, 636 ͑1925͔͒, which we evaluate up to computer precision for the cubic lattices and hcp. The inclusion of three-body terms does not change the preference of hcp over fcc, and zero-point vibrational effects are responsible for the transition from hcp to fcc as shown recently by Rosciszewski et al. ͓Phys. Rev. B 62, 5482 ͑2000͔͒. More precisely, we show that it is the coupling between the harmonic modes which leads to the preference of fcc over hcp, as the simple Einstein approximation of moving an atom in the static field of all other atoms fails to describe this difference accurately. Anharmonicity corrections to the crystal stability are found to be small for argon and krypton. We show that at pressures higher than 15 GPa three-body effects become very important for argon and good agreement is reached with experimental high-pressure density measurements up to 30 GPa, where higher than three-body effects become important. At high pressures we find that fcc is preferred over the hcp structure. Zero-point vibrational effects for the solid can be successfully estimated from an extrapolation of the cluster zero-point vibrational energies with increasing cluster size N. For He, the harmonic zero-point vibrational energy is predicted to be always above the potential energy contribution for all cluster sizes up to the solid state at structures obtained from the two-body force. Here anharmonicity effects are very large which is typical for a quantum solid.
Physical Chemistry Chemical Physics, 2011
Inorganic Chemistry, 2015
The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (e... more The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (element E = N-Bi) were investigated and compared to the group 13 example of GaH2(t-C4H9). With the aid of extensive density functional theory based analysis of atomic and electronic structures at the transition state, we can derive three distinct reaction classes. The gallium compound follows the well-known β-hydride route with participation of an empty p orbital at the metal in a concerted, synchronous fashion, exhibiting a low barrier. For compounds with group 15 elements, we find highly nonsynchronous reactions with high reaction barriers. In the case of nitrogen, a proton-like H atom is transferred via attack of the nitrogen nonbonding electron pair. For the heavier homologues (P-Bi), E-Cα bond breaking occurs first and the H atom does not carry charge at the transition state. The reaction barrier in group 15 homologues is thus determined by the E-Cα bond strength down the group. The results enable a rationale for ligand design for precursors involved in chemical vapor-phase deposition processes because a good ligand needs to stabilize the positive charge at Cα.
The transition from postdoc to Principal Investigator (PI) is a crucial one, and certainly unique... more The transition from postdoc to Principal Investigator (PI) is a crucial one, and certainly unique among the many transitions (high school student-college student, college studentgrad student, grad student-postdoc) in an academic career. We can thus not build on a vast reservoir of personal experiences during the beginning of this phase. Furthermore, although many major universities offer professional development centers, there is no overabundance of courses and seminars you can take to prepare for this step. In the best case, you have a good mentor, but also their advice is (almost by necessity) largely limited to their own experience. In order to provide some hints as to what points you might consider yourself and as a guide for professional development offices, we decided to compile a list of the things that caught us off guard to a certain extent when we started our careers as independent PIs. Naturally, such a list is heavily skewed towards our experience and by no means representative, but we feel that these are recurring themes and sometimes easily avoided with a bit of preparation. Even if some of the points we make are rather obvious, it might be comforting for other young PIs to know that they are not the only ones encountering certain problems. We have structured the points by grouping them into four categories: (i) The challenges of time management; (ii) points regarding personal development; (iii) dealing with students and co-workers and (iv) colleagues and the scientific community. Finally, we compiled some potential solutions and strategies that have been helpful for us and provide our ideas about improving some of the points raised.
Theoretical Chemistry Accounts, 2010
The possible existence of the gas phase cis-and trans-maleate, i.e. completely deprotonated malei... more The possible existence of the gas phase cis-and trans-maleate, i.e. completely deprotonated maleic acid (O 2 C-CH=CH-CO 2 ) 2-, is investigated by density functional (B3LYP) and ab-initio quantum chemical methods (MP2, CCSD(T)) using large basis sets. The calculations reveal that only the trans-isomer is Coulomb stable with respect to electron loss. The results are compared to other previously investigated dicarboxylate dianions of the general form -O 2 C-R-CO 2 with R = C 2 , C 2 X 2 , C 2 X 4 , and C 6 X 4 (X = H, F). Fluorine substitution on the carbon framework helps to stabilize these doubly charged systems, and we predict that all of the aromatic fluorine substituted dicarboxylate dianions are Coulomb stable in the gas phase. Only the highest levels of theory reveal the slight stabilization of both the succinate dianion and the orthoisomer of the phthalic acid dianion in unprecedented agreement with experiments.
ChemPhysChem, 2010
The optimal adsorption modes for the amino acids glycine and proline on the ideal TiO(2)(110) sur... more The optimal adsorption modes for the amino acids glycine and proline on the ideal TiO(2)(110) surface are investigated by using density functional theory (PBE) applying periodic boundary conditions. Binding modes with anionic acid moieties bridging two titanium atoms after transferring a proton to the surface are the most stable configurations for both molecules investigated-similar to previous results for carboxylic acids. In contrast to the latter compounds, amino acids can form hydrogen bonds via the amino group towards the surface-bound proton; this provides an additional stabilisation of 15-20 kJ mol(-1). Zwitterionic binding modes are less stable (by 10-20 kJ mol(-1)) and are less important for proline. Neutral modes are energetically even less favourable. Calculations of vibrational frequencies and core-level shifts complement the adsorption study and provide guidance for future experimental investigations. Control of the computational parameters is crucial for the derivation of accurate results. The layout and thickness of the slab model used are also shown to be decisive factors. Calculations with a different GGA-functional (PW91) provide very similar relative energies, although the absolute energies change by about 20 kJ mol(-1). Results derived with the hybrid functional PBE0 show an even greater stabilisation of the anionic binding modes with respect to the zwitterionic modes. A previously observed discrepancy between experimental and theoretical results for glycine could be solved, although the experimentally proposed free rotation of the C-C bond could not be reproduced.
In an effort to understand the chemical factors that stabilize dianions, experimental and theoret... more In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O2C–CH(OH)–CH(OH)–CO2)2– → (O2C–CH(OH)–CH(OH))•– + CO2 + e– explaining the observed gas-phase instability of this dianion. Further theoretical data
The Journal of Chemical Physics, 2015
The development and first applications of a new periodic energy decomposition analysis (pEDA) sch... more The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the binding energy between two fragments (e.g. the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic and dispersion interaction, Pauli repulsion and orbital relaxation energies. The pEDA presented here for an AO-based implementation can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy and k-space sampling. Four typical bonding scenarios for surface adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H2 on M(001), M = Pd, Cu) and semiconducting (CO and C2H2 on Si(001)c(4x2)) substrates. These examples cover the regimes of metallic, semiconducting and insulating substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence, that the pEDA will be a powerful tool for the analysis of surfaceadsorbate binding in the future, enabling the transfer of concepts like ionic and covalent binding, donor-acceptor interaction, steric repulsion and others to extended systems.
High Performance Computing in Science and Engineering '05, 2006
... Acc. 99 (1998), 391 S [17] EJ Baerends; JA Autschbach; A. Berces; C. Bo; PM Boerrigter; L. Ca... more ... Acc. 99 (1998), 391 S [17] EJ Baerends; JA Autschbach; A. Berces; C. Bo; PM Boerrigter; L. Cavallo; DP Chong; L. Deng; RM Dickson; DE Ellis; L. Fan; TH Fischer; C. Fonseca Guerra; SJA van Gisbergen; JA ... 136 (1987), 52 S [37] Demaison, J.; Hegelund, F.; Burger, H.: In: J. Mol ...
Chemical Science, 2011
ABSTRACT It is shown that vanadium-iminato ligands are more efficient than imidazolidin-2-iminato... more ABSTRACT It is shown that vanadium-iminato ligands are more efficient than imidazolidin-2-iminato substituents to delocalize the spin density from a phosphorus nucleus. However, the latter is stabilizing enough to allow for the isolation and characterization in the liquid and solid states of a neutral phosphinyl radical.
Wiley Interdisciplinary Reviews-Computational Molecular Science, 2011
Physical chemistry chemical physics : PCCP, 2014
The gas phase decomposition reactions of precursor molecules relevant for metal-organic vapour ph... more The gas phase decomposition reactions of precursor molecules relevant for metal-organic vapour phase epitaxy (MOVPE) of semiconductor thin films are investigated by computational methods on the density-functional level as well as on the ab initio (MP2, CCSD(T)) level. A comprehensive reaction catalogue of uni- and bimolecular reactions is presented for triethylgallium (TEG) as well as for tert-butylphosphine (TBP) containing thermodynamic data together with transition state energies. From these energies it can be concluded that TEG is decomposed in the gas phase under MOVPE conditions (T = 400-675 °C, p = 0.05 atm) to GaH3via a series of β-hydride elimination reactions. For elevated temperatures, further decomposition to GaH is thermodynamically accessible. In the case of TBP, the original precursor molecule will be most abundant since all reaction channels exhibit either large barriers or unfavorable thermodynamics. Dispersion-corrected density functional calculations (PBE-D3) provide an accurate description of the reactions investigated in comparison to high level CCSD(T) calculations serving as benchmark values.
Organometallics, 2011
The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents... more The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions.
Chemical Society reviews, Jan 21, 2014
Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the ... more Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the singlet (1)D state behave as bidentate Lewis acids that strongly bind two σ donor ligands L in the donor-acceptor complexes L→E←L. Tetrylones EL2 are divalent E(0) compounds which possess two lone pairs at E. The unique electronic structure of tetrylones (carbones, silylones, germylones, stannylones, plumbylones) clearly distinguishes them from tetrylenes ER2 (carbenes, silylenes, germylenes, stannylenes, plumbylenes) which have electron-sharing bonds R-E-R and only one lone pair at atom E. The different electronic structures of tetrylones and tetrylenes are revealed by charge- and energy decomposition analyses and they become obvious experimentally by a distinctively different chemical reactivity. The unusual structures and chemical behaviour of tetrylones EL2 can be understood in terms of the donor-acceptor interactions L→E←L. Tetrylones are potential donor ligands in main group compou...
Zeitschrift für anorganische und allgemeine Chemie, 2007
The Journal of Physical Chemistry C, 2012
ABSTRACT Vibrational properties of highly ordered crystalline perfluoropentacene (PFP) films epit... more ABSTRACT Vibrational properties of highly ordered crystalline perfluoropentacene (PFP) films epitaxially grown on KCl(100) and NaF(100) substrates have been studied by means of transmission infrared spectroscopy and density functional theory. The different molecular orientations adopted by PFP on both substrates (standing vs lying) and their epitaxial ordering enable precise polarization-resolved measurements along individual crystallographic directions and thus allow an unambiguous experimental determination of the polarization of the IR modes. Computations of the vibrational spectra beyond the single-molecule approximation were employed at the periodic dispersion-corrected density functional level (PBE-D2PBC) and compared with nonperiodic calculations (PBE-D2/def2-TZVPP). Thereby, a detailed mode assignment based on vibrational energies and polarization information was attained. A microscopic explanation for the experimentally observed Davydov splitting of some modes and the IR inactivity of others was derived based on the mutual coupling of the dynamical dipole moments of the two molecules within the unit cell. Experimentally observed modes not covered by our theoretical analysis have been identified as combination bands of IR-active modes coupled to totally symmetric modes of similar displacement patterns. These findings have important implications for future studies on structure and charge transport in organic semiconductors and the validation of theoretical approaches for the modeling of vibrational spectra.
The Journal of Physical Chemistry A, 2012
In an effort to understand the chemical factors that stabilize dianions, experimental and theoret... more In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O 2 C− CH(OH)−CH(OH)−CO 2 ) 2− → (O 2 C−CH(OH)−CH-(OH)) •− + CO 2 + e − explaining the observed gas-phase instability of this dianion. Further theoretical data were collected for the bare dianion, this molecule complexed to water, sodium, and a proton, in both the meso and L forms as well as for the uncomplexed radical anion and neutral diradical. The calculations suggest that the L-tartrate dianion is more thermodynamically stable than the dianion of the meso stereoisomer and that either dianion can be further stabilized by association with a separate species that can help to balance the charge of the molecular complex. Mass spectrometry was then used to measure the energy needed to initiate collisionally induced dissociation of the racemic tartrate dianion and for the proton and sodium adducts of both the racemic and meso form of this molecule. Infrared action spectra of the dianion stereoisomers complexed with sodium were also acquired to determine the influence of the metal ion on the vibrations of the dianions and validate the computationally predicted structures. These experimental data support the theoretical conclusions and highlight the instability of the bare tartrate dianion. From the experimental work, it could also be concluded that the pathway leading to dissociation is under kinetic control because the sodium adduct of the racemic stereoisomer dissociated at lower collisional energy, although it was calculated to be more stable, and that decomposition proceeded via C−C bond dissociation as computationally predicted. Taken together, these data provide insight into the gas-phase stability of the tartrate dianion and highlight the role of adducts in stabilizing this species. Figure 1. Stereoisomers of tartaric acid. Article pubs.acs.org/JPCA
Pure and Applied Chemistry, 2000
Physical Review B, 2006
The many-body expansion V int = ͚ iϽj V ͑2͒ ͑r ij ͒ + ͚ iϽjϽk V ͑3͒ ͑r ij , r ik , r jk ͒ +¯, in ... more The many-body expansion V int = ͚ iϽj V ͑2͒ ͑r ij ͒ + ͚ iϽjϽk V ͑3͒ ͑r ij , r ik , r jk ͒ +¯, in terms of interaction potentials between rare-gas atoms converges fast at distances r Ͼ r HS , with r HS being the hard-sphere radius at the start of the repulsive wall of the interaction potential. Hence, for the solid state where the minimum distance is always above r HS , a reasonable accuracy is already obtained for the lattice parameters and cohesive energies of the rare-gas elements using precise two-body terms. All tested two-body potentials show a preference of the hcp over the fcc structure. We demonstrate that this is always the case for the Lennard-Jones potential. We extend the Lennard-Jones potential to obtain analytical expressions for the lattice parameters, cohesive energy, and bulk modulus using the solid-state parameters of Lennard-Jones and Ingham ͓Proc. R. Soc. London, Ser. A 107, 636 ͑1925͔͒, which we evaluate up to computer precision for the cubic lattices and hcp. The inclusion of three-body terms does not change the preference of hcp over fcc, and zero-point vibrational effects are responsible for the transition from hcp to fcc as shown recently by Rosciszewski et al. ͓Phys. Rev. B 62, 5482 ͑2000͔͒. More precisely, we show that it is the coupling between the harmonic modes which leads to the preference of fcc over hcp, as the simple Einstein approximation of moving an atom in the static field of all other atoms fails to describe this difference accurately. Anharmonicity corrections to the crystal stability are found to be small for argon and krypton. We show that at pressures higher than 15 GPa three-body effects become very important for argon and good agreement is reached with experimental high-pressure density measurements up to 30 GPa, where higher than three-body effects become important. At high pressures we find that fcc is preferred over the hcp structure. Zero-point vibrational effects for the solid can be successfully estimated from an extrapolation of the cluster zero-point vibrational energies with increasing cluster size N. For He, the harmonic zero-point vibrational energy is predicted to be always above the potential energy contribution for all cluster sizes up to the solid state at structures obtained from the two-body force. Here anharmonicity effects are very large which is typical for a quantum solid.
Physical Chemistry Chemical Physics, 2011