Papers by Peter Schwerdfeger
Chirality, 2010
Parity violation (PV) effects in chiral molecules have so far never been experimentally observed.... more Parity violation (PV) effects in chiral molecules have so far never been experimentally observed. To take up this challenge, a consortium of physicists, chemists, theoreticians, and spectroscopists has been established and aims at measuring PV energy differences between two enantiomers by using high‐resolution laser spectroscopy. In this article, we present our common strategy to reach this goal, the progress accomplished in the diverse areas, and point out directions for future PV observations. The work of André Collet on bromochlorofluoromethane (1) enantiomers, their synthesis, and their chiral recognition by cryptophanes made feasible the first generation of experiments presented in this article. Chirality, 2010. © 2010 Wiley‐Liss, Inc.
d2 Complexes of tungsten containing p-toluonitrile as a four- or two-electron donor and oxidative addition giving the two-electron donor acylimido ligand NCOC6H4Me-4
Journal of the Chemical Society, Dalton Transactions, 1997
... The NMR spectra thus indi-cate that the four methyl groups are diastereotopic which is also a... more ... The NMR spectra thus indi-cate that the four methyl groups are diastereotopic which is also a spectral feature of [WCl2(NC6H3Pri 2-2,6)(HC2Ph)(PMe3)2].4 The nitrile carbon resonance for 2 appeared as a doublet of doublets centred at δ 178.9 which is in the region found for ...
Trichloro monophenoxide complexes of titanium(IV)
Journal of the Chemical Society, Dalton Transactions, 2000
ABSTRACT Thermalisation of TiCl4 and phenol (1∶1) in toluene gave [TiCl3(OC6H5)] 1. The more solu... more ABSTRACT Thermalisation of TiCl4 and phenol (1∶1) in toluene gave [TiCl3(OC6H5)] 1. The more soluble complex [TiCl3(OC6H4CMe3-4)] 2 is monomeric in benzene and reacts with 4,4′-dimethyl-2,2′-bipyridyl (dmbipy) to give mer-[TiCl3(OC6H4CMe3-4)(dmbipy)] 3 and the disproportionation product [TiCl2(OC6H4CMe3-4)2(dmbipy)]. The complex [TiCl3(OC6H2Me3-2,4,6)] 4 is monomeric in benzene whereas [TiCl3(OC6H3Pri2-2,6)] 5 partially disproportionates in solution into [TiCl2(OC6H3Pri2-2,6)2] and reacts with dmbipy to give mer-[TiCl3(OC6H3Pri2-2,6)(dmbipy)] 6 and [TiCl2(OC6H3Pri2-2,6)2(dmbipy)]. Thermalisation of 2,6-di-tert-butyl-4-methylphenol and TiCl4 in toluene caused debutylation but [TiCl3{OC6H2(CMe3)2-2,6-Me-4}] 7 forms in light petroleum (bp range 40–60 °C). Complex 7 is monomeric in benzene and does not form adducts with dmbipy or other sigma donors. A crystal structure determination of 7 showed a monomer with distorted tetrahedral co-ordination, a Ti–O bond length of 1.750(2) Å and Ti–Cl bonds longer than in TiCl4 but shorter than in [TiCl3(C5H5)] or [TiCl3{C5H3(CMe3)2-1,3}]. 2,4,6-Tri-tert-butylphenol debutylates when thermalised with TiCl4 in toluene giving [TiCl3{OC6H4(CMe3)2-2,4} ] 8. The complexes [TiCl3{OC6H2(CMe3)2-2,6-OMe-4}] 9, [TiCl3(OC6H3CMe3-2-Me-4)] 10, [TiCl3(OC6H4Ph-2)] 11 and the 1-naphthoxide complex [TiCl3(OC10H7)] 12 were also prepared. Density functional calculations performed on the models 4 and [TiCl3(OMe)] showed both lone pairs on oxygen donate electron density to titanium but O(2p)-to-CC (π*) donation weakens the Ti–O interaction in the phenoxide complex; Cl(2p)-to-Ti(3d) donation is much reduced in the methoxide complex. The system [TiCl3(OC6H4CMe3-4)]/AlMe3 is 280 times more active than [TiCl3Cp] (Cp = cyclopentadienyl)/AlMe3 for low pressure (6 psi) ethylene polymerisation but 1//3 less active than TiCl4/AlMe3.
PHYS 541-Gold clusters: Convergence of the n-body expansion of the interaction energy
Inorganic Chemistry, 2009
The kinetic and thermodynamic stabilities of the group 13 hydrides EH 3 (E = B, Al, Ga, In, Tl, E... more The kinetic and thermodynamic stabilities of the group 13 hydrides EH 3 (E = B, Al, Ga, In, Tl, E113) are investigated by relativistic density functional and wave function based theories. The unimolecular decomposition of EH 3 f EH þ H 2 becomes energetically more favorable going down the Group 13 elements, with the H 2 -abstraction of InH 3 , TlH 3 , and (E113)H 3 (E113: element with nuclear charge 113) being exothermic. In accordance with the Hammond-Leffler postulate, the activation barrier for the dissociation process decreases accordingly going down the group 13 elements in the periodic table shifting to an early transition state, with activation energies ranging from 88.4 kcal/mol for BH 3 to 41.3 kcal/mol for TlH 3 and only 21.6 kcal/mol for (E113)H 3 at the scalar relativistic coupled cluster level of theory. For both TlH 3 and (E113)H 3 we investigated spin-orbit effects using Dirac-Hartree-Fock and second-order Møller-Plesset theory to account for electron correlation. For (E113)H, spin-orbit coupling results in a chemically inert closed 7p 1/2 -shell, thus reducing the stability of the higher oxidation state even further. We also investigated the known organothallium compound Tl(CH 3 ) 3 , which is thermodynamically unstable similar to TlH 3 , but kinetically very stable with an activation barrier of 57.1 kcal/mol.
European Journal of Inorganic Chemistry, 2005
Thermalisation of TiCl4 and two equivalents of a phenol in toluene is found to be the best prepar... more Thermalisation of TiCl4 and two equivalents of a phenol in toluene is found to be the best preparative method for quantitative yields of a variety of dichlorobis(phenoxo) complexes. [TiCl2(OC6H4CMe3‐4)2] (1) is monomeric in benzene, a phenoxo‐bridged dimer in the solid state and undergoes coordination expansion with 4,4'‐dimethyl‐2,2′‐bipyridine (dmbipy) to give [TiCl2(OC6H4CMe3‐4)2(dmbipy)] (2). Also monomeric are [TiCl2(OC6H2Me3‐2,4,6)2] (3) and [TiCl2(OC6H3iPr2‐2,6)2] (5) which expand their coordination with dmbipy to give [TiCl2(OC6H2Me3‐2,4,6)2(dmbipy)] (4) and [TiCl2(OC6H3iPr2‐2,6)2(dmbipy)] (6). In contrast [TiCl2(OC6H2{CMe3}2‐2,6‐Me‐4)2] (7) is only partially formed by the thermolysis reaction and does not coordinatively expand with dmbipy. [TiCl2(OC6H3Me2‐2,4)2] (8) is monomeric in benzene and reacts to form [TiCl2(OC6H3Me2‐2,4)2(dmbipy)] (9). [TiCl2(OC6H3{CMe3}2‐2,4)2] (10) forms along with the tri‐phenoxo complex [TiCl{OC6H3(CMe3)2‐2,4}3]. [TiCl2(OC6H3CMe3‐2‐Me‐6)2] (...
Angewandte Chemie International Edition, 2007
Physical Review A, 2007
The many-body expansion of the interaction potential between atoms and molecules is analyzed in d... more The many-body expansion of the interaction potential between atoms and molecules is analyzed in detail for different types of interactions involving up to seven atoms. Elementary clusters of Ar, Na, Si, and, in particular, Au are studied, using first-principles wave-function-and density-functional-based methods to obtain the individual n-body contributions to the interaction energies. With increasing atom number the many-body expansion converges rapidly only for long-range weak interactions. Large oscillatory behavior is observed for other types of interactions. This is consistent with the fact that Au clusters up to a certain size prefer planar structures over the more compact three-dimensional Lennard-Jones-type structures. Several Au model potentials and semiempirical PM6 theory are investigated for their ability to reproduce the quantum results. We further investigate small water clusters as prototypes of hydrogen-bonded systems. Here, the many-body expansion converges rapidly, reflecting the localized nature of the hydrogen bond and justifying the use of two-body potentials to describe water-water interactions. The question of whether electron correlation contributions can be successfully modeled by a many-body interaction potential is also addressed.
Chemical Physics Letters, 2004
The C-C*-CO bending mode in camphor (C* denotes a chiral carbon) as originally investigated for p... more The C-C*-CO bending mode in camphor (C* denotes a chiral carbon) as originally investigated for parity violation effects by Arimondo et al. [Opt. Commun. 23 (1977) 369] lies in the CO 2 laser frequency range with the most intense transition at 1045 cm À1 . The vibrational spectrum of camphor is, therefore, reinvestigated by ab initio and density functional calculations and compared with experimental results. This provides the basis for a local mode analysis which reveals that the C-C*-CO bending mode has only minute parity violation contributions (<10 À5 Hz) to vibrational transitions far below the current detection limit of high resolution spectroscopy.
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.
A Comparative Computational Study of Cationic Coinage Metal−Ethylene Complexes (C 2 H 4 )M + (M = Cu, Ag, and Au)
The Journal of Physical Chemistry, 1996
The cationic (C 2 H 4 )M + complexes (M = Cu, Ag, and Au) have been examined by different ab init... more The cationic (C 2 H 4 )M + complexes (M = Cu, Ag, and Au) have been examined by different ab initio molecular orbital, density functional (DFT), and density functional/Hartree−Fock (DFT/HF) hybrid methods using relativistic effective core potentials and a quasi-relativistic ...
High-valent diphenylacetylene complexes of tungsten
Journal of the Chemical Society, Dalton Transactions, 1995
ABSTRACT The W(4f7//2) binding energy of [{WCl4(PhC2Ph)}2]1 obtained by X-ray photoelectron spect... more ABSTRACT The W(4f7//2) binding energy of [{WCl4(PhC2Ph)}2]1 obtained by X-ray photoelectron spectroscopy is similar to that of [{WCl4(NPh)}2] and is consistent with a do tungsten(VI) formulation. The reaction of complex 1 and [NEt4][WCl5(PhC2Ph)]2 with NaOH–EtOH gave cis-stilbene, indicating considerable electron transfer from the metal to the co-ordinated alkyne. Reduction of complex 1 with 2 equivalents of sodium–mercury amalgam in the presence of phosphines gave the complexes [WCl3(PhC2Ph)L2](L = PMe3, PMe2Ph or PMePh2) with magnetic moments and W(4f7//2) binding energies similar to those of the d1 tungsten(V) organoimido complex [WCl3(NPh)(PMe3)2]. Decomposition of the alkyne complexes with NaOH–EtOH again gave cis-stilbene. The crystal structure of [WCl3(PhC2Ph)(PMe3)2]3 has been determined. The W–Cl bond trans to the alkyne ligand is long [2.479(3)Å], and the W–C bond lengths [2.011(13) and 2.038(12)Å] indicate a four-electron-donor alkyne ligand. The geometry is similar to that of [WCl3(NPh)(PMe3)2]. Reduction of [{WCl4(PhC2Ph)}2] using 4 equivalents of sodium–mercury amalgam in the presence of phosphines gave the complexes [WCl2(PhC2Ph)L3](L = PMe3 or PMe2Ph) which again produced cis-stilbene on decomposition with NaOH–EtOH. The acetylenic carbon resonance at δ 223.15 in the 13C-{1H} NMR spectrum of [WCl2(PhC2Ph)(PMe3)3]6 is also indicative of a four-electron-donor alkyne ligand. Its W(4f7//2) binding energy is similar to [WCl2(NPh)(PMe3)3] and is consistent with tungsten(IV). A crystal structure of complex 6 shows a similar ligand geometry to [WCl2(NPh)(PMe3)3], and the W–C bond lengths [2.019(11) and 2.006(11)Å] indicate a four-electron-donor alkyne ligand. Hartree–Fock and scattered wave Xα calculations have been performed on the model complexes [WCl5(HC2H)]–8, [WCl3(HC2H)(PH3)2]9 and [WCl2(HC2H)(PH3)3]10. Molecular orbital and population analyses indicated that the acetylene–tungsten bond in each involves W(5dπ)→ HC2H(π*) back donation as well as HC2H(π)→ W(5dσ) and HC2H(π⊥)→ W(5dπ) forward donation, consistent with a four-electron-donor alkyne formalism. Electron withdrawal from the tungesten to the more electronegative Cl ligand in complexes 8 and 9 is minimised by rotation of the alkyne away from the meridional vectors. In complex 10 the HC2H(π⊥)→ W(5dπ) donation and phosphine contributions compensate and no rotation is observed. The total d atomic orbital population of complex 8 is close to that of WCl6, and populations of complexes 9 and 10 step up linearly from this. The computational results support the experimental evidence that [{WCl4(PhC2Ph)}2]1, [WCl3(PhC2Ph)(PMe3)2]3 and [WCl2(PhC2Ph)(PMe3)3]6 are complexes of tungsten-(VI), -(V) and -(IV) respectively.
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.
Polyhedron, 2007
Group 7 trioxides LRO 3 with perfluorated ligands L (L = CF 3 , C 5 F 5 and C 6 F 5) are investig... more Group 7 trioxides LRO 3 with perfluorated ligands L (L = CF 3 , C 5 F 5 and C 6 F 5) are investigated using density based (BP86) and wavefunction based (MP2) methods together with energy-adjusted scalar relativistic pseudopotentials for the metal atoms Mn, Tc and Re. The C 6 F 5 compounds have short metal-carbon bond distances and are more stable than the g 1-C 5 F 5 and the CF 3 compounds. The perfluorinated cyclopentadienyl compounds, C 5 F 5 MO 3 , all are g 1 coordinated in contrast to the C 5 Me 5 MO 3 homologues. Our calculations indicate that C 6 F 5 MnO 3 might be a stable complex and therefore a promising target for future synthesis.
Ground State Electron Configuration of Element 111
Physical Review Letters, 1994
The low-lying electronic states of element 111 are investigated by the relativistic coupled-clust... more The low-lying electronic states of element 111 are investigated by the relativistic coupled-cluster method based on the Dirac-Coulomb-Breit Hamiltonian. A large basis set (26s21p16d9f7g5h) of Gaussian-type orbitals is used. In contrast to the lighter group 11 ...
Search for a Parity-Violating Energy Difference between Enantiomers of a Chiral Iron Complex
Physical Review Letters, 2000
Mossbauer spectra for l and d enantiomers of the Fe(phen)3Sb2(C4H2O6)(2);8H(2)O complex are repor... more Mossbauer spectra for l and d enantiomers of the Fe(phen)3Sb2(C4H2O6)(2);8H(2)O complex are reported. Four independent experiments show a small but reproducible energy shift of the Fe-Mossbauer spectra for the two enantiomers of 0.004+/-0. 002 mm/sec ( 1.9x10(-10) eV). This exceedingly small energy difference is comparable to that predicted by the parity-violating energy difference (PVED) using a Z6.2 scaling law applied to low Z ( Z = 6) molecules. Theoretical calculations suggest that the PVED for the Fe(phen)2+3 moiety should be smaller than this estimate, however, PVED effects of the chiral antimony tartrates are not taken into account.
SeOClI: A promising candidate for the detection of parity violation in chiral molecules
Physical Review A, 2008
... [13] M. Quack, Angew. Chem., Int. Ed. 41, 4619 (2002), and ref-erences therein. [14] BG Levi,... more ... [13] M. Quack, Angew. Chem., Int. Ed. 41, 4619 (2002), and ref-erences therein. [14] BG Levi, Phys. Today 53(9), 46 (2000). ... Phys. 119, 11113 (2003). [37] D. Gregory, L. Hargittai, and M. Kolonits, J. Mol. Struct. 31, 261 (1976). [38] T. Saue, T. Enevoldsen, T. Helgaker, HJ Aa. ...
Physical Chemistry Chemical Physics, 2011
The following Tables contain the optimized structures from VASP and Gaussian03 calculations. Stru... more The following Tables contain the optimized structures from VASP and Gaussian03 calculations. Structures from periodic boundary condition(PBC)-calculations are given in a fractional coordinate format suitable for VASP (CONTCAR). Structures from non-PBC calculations are given in cartesian coordinates. Length unit is Å throughout and SCF-energies are given in eV for PBC-calculations and a.u. for non-PBC calculations.
Physical Chemistry Chemical Physics, 2011
Reply to the 'Comment on ''Theoretical investigations into the enantiomeric and racemic forms of ... more Reply to the 'Comment on ''Theoretical investigations into the enantiomeric and racemic forms of a-(trifluoromethyl)lactic acid'''
Organometallics, 1990
In a recent paper we presented Hartree-Fock (HF) calculations for aliphatic organothallium compou... more In a recent paper we presented Hartree-Fock (HF) calculations for aliphatic organothallium compounds. The diagonal HF force constants obtained from a Fletcher-Powell geometry optimization are now used for a normal-mode analysis of TlCH,, Tl(CH,),+, T1(CH3),, T1(CHJ2Br, and Tl(CH3)c. In order to calculate frequencies comparable to experimental values, the HF force field has been scaled by using scaling factors obtained from experimental infrared and Raman measurements on T1(CH3)2+ and TlBr. The vibrational spectra of Tl(CH3)2+ were remeasured (infrared and Raman) in order to obtain an accurate force field. Predictions are made for the vibrational spectrum of the as yet undetected TlCH, molecule. Experimental infrared and Raman results for T1(CH3), compare reasonably well with our calculated frequencies (experimental v,,(Tl-C) = 450 cm-', v,,(Tl-C) = 465 cm-l, v,,(C-H) = 2917 cm-l, v, , (C-H) = 3020 cm-l; scaled HF u,,(Tl-C) = 488 cm-', v,,(Tl-C) = 514 cm-', vSp(C-H) = 2892 cm-l, Y , (C-H) = 2999 cm-l). Relativistic and correlation effects are analyzed for the vibrational frequencies ~f i l (C H ,)~+ .
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Papers by Peter Schwerdfeger