<Emphasis Type="Italic">Ab Initio</Emphasis> calculations of 3-(trichlorogermyl)propanoylamide structure and nature of its Ge←O coordination bond

Calculations of 3-(trichlorogermyl)propanoylamide molecule containing a Ge←O coordination bond were performed by RHF/6-31G(d) method with full and partial geometry optimization. Its total energy 2.22 kcal mol⁻¹ is lower than that of the molecule with tetracoordinated germanium atoms. Germanium and oxygen atoms initiate the formation of a coordination Ge←O bond in this molecule and are conductors of the electron density transfer from the atoms nearest to the oxygen on the atoms of the germanium coordination polyhedron. No electron density transfer occurs from the oxygen atom to germanium. Upon decrease in the Ge...O distance the axial Ge-Cl bond is polarized much stronger than the equatorial bonds. In the crystalline state of the substance these molecules are fixed in an energetically unfavorable structure.     

ab initio Calculation of the stereoelectronic structure of 1-(1-trichlorogermylethyl)-pyrrolidin-2-one*

RHF/6-31G(d) and MP2/6-31G(d) calculations were carried out to study the stereoelectronic structure of 1-(1-trichlorogermylethyl)pyrrolidin-2-one with a pentacoordinated germanium atom. These results were compared with the X-ray diffraction structural analysis data. Upon formation of the Ge ← O coordination bond in this molecule, the electron density of all the atoms of the coordination polyhedron of the germanium atom, including the oxygen atom, increases, especially the axial chlorine atom, while the electron density of the germanium, nitrogen, and carbonyl group carbon atoms decreases. Different polarization of all three valence p-orbitals of each Cl atom of this molecule was established. ³⁵Cl nuclear quadrupole resonance spectrum parameters were evaluated. The molecule also has stable form, in which the germanium atom is tetracoordinated. The total energy of this form is 2.7 kcal/mol higher than for the structure with a pentacoordinated germanium atom.     

Molecular Structure of 1-Germatrahol and its Complex With Chloroform

The crystal structures of anhydrous 1-germatranol and its complex with HCCl₃ are centrosymmetrical dimers because of their intermolecular hydrogen bonds. In the germatranol crystal, the axial and equatorial oxygen atoms of its two molecules are hydrogen bonded into an eight-membered coordination cycle. In the complex with HCCl₃, the two molecules of germatranol are likewise linked in dimers, and both axial oxygen atoms are H bonded with HCCl₃. In the investigated structures, the axial Ge—O bond is shorter than the equatorial ones. Depending on the number and strength of the hydrogen bonds, the interatomic Ge—O and Ge ← N distances change markedly. The quantitative estimates of the H bond energy are obtained from quantum chemical calculations of the model systems containing 1-germatranol and HCCl₃ molecules.     

Stereoelectronic structure of 3-(trichlorogermyl)propionic acid by the results of <Emphasis Type="Italic">ab initio</Emphasis> calculations

Two structures of the 3-(trichlorogermyl)propionic acid molecule and its dimer were calculated by the RHF/6-31G(d) method with the full geometry optimization. The structure with pentacoordinated germanium atom is by 4.71 kcal mol^?1 more favorable than that with tetracoordinated germanium. The strength of coordination bond in the first structure increases with the absolute values of charge on the Ge and O coordination centers. The relatively small values of these charges result in a weak coordination bond. In the first structure, this bond is weaker than in the dimer, since the Ge…O distance in it (3.016 Å) is larger than in the latter (2.898 Å). This bond is formed due to the rapproachment of the Ge and O coordination centers at their electrostatic interaction. This provides the transfer of electron density from the atoms of the donor fragment of the molecule to the atoms of the germanium coordination polyhedron. The coordination centers serve as the conductors for the electron density transfer.     

Structure of 2-methyl-3-(trichlorogermyl)propionic acid N,N-dimethylamide and the nature of the Ge←O coordination bond according to the ab initio calculation

Calculations of the molecule of 2-methyl-3-(trichlorogermyl)propionic acid N,N-dimethylamide with full and partial optimization of its geometry were performed by the RHF/6-31G(d) method. The total energy of this molecule which includes a pentacoordinated germanium atom (I) is by 3.84 kcal mol^?1 lower than if it contains a tetrakoordinated germanium (II). The mutual approach of Ge and O coordination centers as a result of their electrostatic interactions in the molecule (I) is shown to result in the formation of a Ge←O coordination bond, which provides an electron density transfer from the peripheral atoms of the donor fragment of the molecule to the atoms of the germanium coordination polyhedron. The Ge and O coordination centers of the molecule serve as conductors of the electron density. At the formation of Ge←O bond the electron density on the oxygen atom increases, while on germanium decreases.     

The molecular and electronic structure features of silatranes, germatranes, and their carbon analogs

Molecular geometries of fifty-six metallatranes N(CH₂CH₂Y)₃M-X and fifty-six carbon analogs HC(CH₂CH₂Y)₃M-X (M = Si, Ge; X = H, Me, OH, F; Y = CH₂, O, NH, NMe, NSiMe₃, PH, S) were optimized by the DFT method. Correlations between changes in the bond orbital populations, electron density ρ(r), electron density laplacian ∇²ρ(r), |λ₁|/λ₃ ratio, electronic energy density E(r), bond lengths, and displacement of the central atom from the plane of three equatorial substituents and the nature of substituents X and Y were studied. As the number of electronegative substituents at the central atom increases, the M←N, M-X, and M-Y bond lengths decrease, while the M←N bond strength and the electron density at critical points of the M←N, M-X, and M-Y bonds increase. An increase in electronegativity of a substituent (X or Y) is accompanied by a decrease in the ionicities of the other bonds (M-X, M-Y, and M←N) formed by the central atom (Si, Ge). A new molecular orbital diagram for bond formation is proposed, which takes into account the interaction of all five substituents at the central atom (M = Si, Ge) in atrane molecules. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 448–460, March, 2006.     

Crystal and molecular structures of six-coordinate germanium difluorides and dibromides containing lactamomethyl C,O-chelating ligands

The structures of (O−Ge)-bischelate bis(lactamomethyl)difluoro- and-dibromogermanes [L⁽ⁿ⁾]₂GeX₂, where L is the bidentate lactamomethyl C,O-chelating ligand,n=5–7 (the size of the lactam ring), and X=F or Br, were studied by X-ray diffraction analysis. The six-coordinate Ge atom in these compounds is involved in two hypervalent X−Ge−O bonds whose parameters are compared with the corresponding values in analogous dichlorides and five-coordinate Ge derivatives. On going from difluorides to dichlorides and then to dibromides, the coordination environment about the Ge atom approaches the ideal octahedron. An analogous effect is observed as the size of the lactam ring increases. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1799–1805, October, 2000.     

Quantum-chemical Investigation of the Hyprevalent Intramolecular Coordination X←N (X = C,Si, Ge) in Quasimonocyclic Models of IVa Group Atranes

The structure and the pentacoordination effect in quasimonocyclic models of IVa group atranes were investigated by ab initio[MP2 (full) /6-311+G **] and the density functional [B3LYP/6-311+G **] quantum chemical calculations. The calculations revealed considerable stabilization of the quasimonocyclic conformations relative to their free-of-strain trans-s-transconformations, which is caused by the formation of secondary (R)XN (X=C, Si, Ge) bonds of the hypervalent type. The strength of the intramolecular (R)XN coordination increases in the order X=C, Si, Ge. The nature of attractive (R)XN coordination is determined by donor-acceptor interaction of the nitrogen lone electron pair and antibonding orbital which primary localize at the X-R bond. Energy of X ··· N (X=Si, Ge) contact is about 3-7 kcal mol^-1.     

Unusual crystal and molecular structure of the 1-(1-silatranylmethyl)-3,5-dimethylpyrazole complex with zinc dichloride

The crystal and molecular structure of a 1-(1-silatranylmethyl)-3,5-dimethylpyrazole complex with zinc dichloride (I) is determined by XRD. The coordination polyhedron of the zinc atom is a tetrahedron formed by two covalent Zn-Cl bonds and coordination Zn ← N and Zn ← O bonds. Compound I is the first example of how an endocyclic oxygen atom of the silatranyl fragment participates in the coordination of the metal atom with the formation of a six-membered heterocycle.     

The structure of organic derivatives of hexacoordinated germanium. (O→Ge) chelated bis-(2-oxo-1-hexahydroazepinylmethyl)difluorogermane and bis-(2-oxo-1-hexahydroazepinylmethyl)fluorogermane tetrafluoroborate

Two fluoro derivatives of hexacoordinated germanium containing chelated 2-oxo-1-hexahydroazepinylmethyl ligands were investigated by X-ray diffraction analysis. The coordination polyhedron of the Ge atom in difluoride1 is a somewhat distorted octahedron with the following bond lengths (Å): Ge-F 1.799(2), GeO 2.185(3), and Ge-C 1.945(4). Tetrafluoroborate 2 has an ionic structure; the valence environment of the Ge atom is a distorted trigonal bipyramid open in the direction of the BF ₄ ^– anion. The bond lengths in 2 are: Ge-F 1.792(8), GeO 2.001(4), and Ge-C 1.937(9) Å; the Ge...F(anion) distances are 3.43(1) and 3.68(1) Å. Analysis of the geometry of1,2, and related structures containing hexa-coordinated germanium shows that the parameters of their hypervalent moieties are related to each other by dependences similar to those observed in compounds of pentacoordinated Si and Ge.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1427–1431, August, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (project No 93-03-4855).     

Spatial and electronic structure and 35Cl NQR parameters of ethyl(trichlorogermyl) propionate according to Ab initio calculations

Two stable structures of ethyl(trichlorogermyl) propionate have been studied by RHF/6-31G(d) and MP2/6-31G(d) quantum-chemical caclulation with full geometry optimization. The structure with pentacoordinated Ge atom has been more stable than that with tetracoordinated Ge atom. Based on the computation results, the frequencies of ³⁵Cl nuclear quadrupole resonance of the studied compound with pentacoordinated Ge atom has been estimated, it has been in satisfactory agreement with the experimental data. Additionally, the calculations by means of the RHF/6-31G(d) method have been performed at various fixed Ge…O interatomic distances. When the Ge and O coordination centers get closer, both the positive charge on Ge and the negative charge on O increase. The electron density shifts from Ge atom to the axial Cl atom, and the electron density shifst from the carbonyl C atom to the carbonyl oxygen atom. The electron density charge trasfer from O to Ge does not occur.     

Effects of substituents and n-donors on the energies of Si←N,Si←O,and Si=C bonds in hypervalent silenes

The effect of the nature of substituents at sp²-hybridized silicon atom in the R₂Si=CH₂ (R = SiH₃, H, Me, OH, Cl, F) molecules on the structure and energy characteristics of complexes of these molecules with ammonia, trimethylamine, and tetrahydrofuran was studied by the ab initio (MP4/6-311G(d)//MP2/6-31G(d)+ZPE) method. As the electronegativity, χ, of the substituent R increases, the coordination bond energies, D(Si← N(O)), increase from 4.7 to 25.9 kcal mol⁻¹ for the complexes of R₂Si=CH₂ with NH₃, from 10.6 to 37.1 kcal mol⁻¹ for the complexes with Me₃N, and from 5.0 to 22.2 kcal mol⁻¹ for the complexes with THF. The n-donor ability changes as follows: THF ≤ NH₃ < Me₃N. The calculated barrier to hindered internal rotation about the silicon—carbon double bond was used as a measure of the Si=C π-bond energy. As χ increases, the rotational barriers decrease from 18.9 to 5.2 kcal mol⁻¹ for the complexes with NH₃ and from 16.9 to 5.7 kcal mol⁻¹ for the complexes with Me₃N. The lowering of rotational barriers occurs in parallel to the decrease in D _π(Si=C) we have established earlier for free silenes. On the average, the D _π(Si=C) energy decreases by ∼25 kcal mol⁻¹ for NH₃· R₂Si=CH₂ and Me₃N·R₂Si=CH₂. The D(Si←N) values for the R₂Si=CH₂· 2Me₃N complexes are 11.4 (R = H) and 24.3 kcal mol⁻¹ (R = F). sp²-Hybridized silicon atom can form transannular coordination bonds in 1,1-bis[N-(dimethylamino)acetimidato]silene (6). The open form (I) of molecule 6 is 35.1 and 43.5 kcal mol⁻¹ less stable than the cyclic (II, one transannular Si←N bond) and bicyclic (III, two transannular Si←N bonds) forms of this molecule, respectively. The D(Si←N) energy for structure III was estimated at 21.8 kcal mol⁻¹. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1952–1961, September, 2005.     

Vibrational spectra and structural features of carbene analogs ElII(OCH2CH2NMe2)2 and ClElIIOCH2CH2NMe2 (ElII = Ge, Sn, Pb)

Vibrational spectra of compounds of divalent Group 14 elements El^II(OCH₂CH₂NMe₂)₂ with El^II = Ge (1), Sn (2), Pb (3) and ClEl^IIOCH₂CH₂NMe₂ with El^II = Ge (4) and Sn (5) were measured for the first time and analyzed within the framework of DFT calclations. Monomeric compounds 1 and 2 whose molecules are stabilized only through intramolecular coordination were confirmed to be isostructural. Unlike 1 and 2, plumbylene 3 is a polymer in both solution and the crystalline state; the latter was confirmed by X-ray diffraction analysis. The ν^s _C-N stretching frequency in the CH₂NMe₂ fragment was shown to decrease by 80–100 cm⁻¹ owing to the formation of the coordination bond El←N. To elucidate the mechanism of a dynamic flip-flop process suggested earlier based on the broadening of some signals in the NMR spectra of compounds 1 and 4, the Raman spectra of solutions of compounds 1 and 2 in THF and Py were obtained. These experiments revealed no equilibrium with participation of a stable form with one coordination bond El←N cleaved along with the starting molecule. This is consistent with the results of the corresponding quantum chemical calculations of thermo-dynamic parameters. A somewhat different, more probable mechanism of the dynamic process was proposed, which involves an overturn of the CH₂NMe₂ fragment with cleavage of the El←N bond in the transition state only.     

Study on the transannular bond formation and hypercoordination in tin and germanium spirometallocanes

D(CH₂CH₂S)₂MSNH(C₆H₄) (M = Ge, Sn; D = O, S) spirocycles were synthesized to analyze the influence of the decrease of the radius of the metal and the change of the hardness of donor atom on the strength of the transannular bond and the hypercoordination of group 14 elements. The compounds were characterized by IR, Raman and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy, EI mass spectrometry and elemental analysis. Monocrystal X-ray diffraction analyses were made for the germanium compounds. The germaspirocycles were five-coordinated and had distorted trigonal bipyramid geometry. In contrast with most of the reported analogous germocanes, the transannular bond is stronger when the donor atom is oxygen, rather than sulfur. O(CH₂CH₂S)₂GeSNH(C₆H₄) exhibits an intramolecular hydrogen bond formation between the amine group and the transannular oxygen. The presence of this hydrogen bond determines whether the sulfur (O?Ge–S) or the nitrogen (S?Ge–N) of the five-member ring is the axial atom. According to the ¹¹⁹Sn chemical shift, both stannospirocycles were five-coordinated and therefore the presence of the transannular interaction in solution could be suggested.     

Quantum-chemical study of chlorophosphoranes: I. Structure of the (C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>PCl<Subscript>3</Subscript> molecule in gaseous and crystalline states

The quantum-chemical calculations of the (C₆H₅)₂PCl₃ molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of ³⁵Cl and the parameters of asymmetry of the of electric field gradient on the ³⁵Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of ³⁵Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the ³⁵Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.     

Geometry of intramolecular silicon complexes: an ab initio estimation of the sensitivity to the effect of medium. (Aroyloxymethyl)trifluorosilanes

The effect of medium on the geometry of the (benzoyloxymethyl)trifluorosilane (1) molecule was studied by the HF and MP2 methods with the 6-31G(d), 6-311G(d), and 6-311+G(d,p) basis sets, as well as using the Onsager SCRF model, the PCM approach, and the data of X-ray diffraction study. Molecule 1 has a low complexation energy (5.4 kcal mol^–1 according to MP2(Full)/6-31G(d)+ZPE calculations and 6.8 kcal mol^–1 according to IR spectroscopy data), while its geometric parameters are the least sensitive to the effects of medium among all hypervalent silicon compounds studied to date. Nevertheless, the results obtained revealed a pronounced deformation of the SiO coordination bond in 1 on going from the gas phase to the polar solution and crystal. This serves as a theoretical substantiation of the hypothesis that substantial changes in the IR and NMR spectral characteristics of the (O—Si)-chelate (aroyloxymethyl)trifluorosilanes upon variation of external factors are due to geometric reasons. Analysis of the electron density distribution according to Bader indicates that the SiO bond in molecule 1 can be treated as a covalent bond of high polarity.     

Hypervalent Intramolecular X←N (X = C,Si, Ge) Coordination in Atranes: Quantum-Chemical Study

The structure and pentacoordination effect in atranes containig Group IVa element were studied ab initio [MP2(full)/6-31G**] and in terms of the density functional theory [B3LYP/6-311+G**]. Stabiliza- tion of these compounds is determined mainly by the secondary hypervalent (R)XN bond (X = C, Si, Ge), whose strength increases in the series X = C, Si, Ge. Attractive (R)XN interaction originates from donation of unshared electron pair on the nitrogen atom to the antibonding ^* _XR orbital.     

A Metal‐Containing N‐Heterocyclic Germylene Based on an Oxalamidine Framework

A metal‐containing N‐heterocyclic germylene based on a N‐mesityl (Mes)‐substituted oxalamidine framework is reported. The precursor (MesN=)₂C–C(–N(H)Mes)₂ ( 1 H₂) was converted into its rhodium complex [Rh(κ²N‐ 1 H₂)(cod)][OTf] ( 2 ) (cod = 1,5‐cyclooctadiene; OTf = triflate) in 62 % isolated yield. Subsequent reaction of 2 with Ge{N(SiMe₃)₂}₂ gave the crystalline N‐heterocyclic germylene [Rh(cod)(μ‐ 1 )Ge][OTf] ( 3 ) in 50 % yield. The compounds under study were fully characterized by various methods, also including X‐ray crystallographic studies on single crystals of 2 and 3 . Density functional theory (DFT) calculations revealed that π conjugation in the bridging oxalamidine framework is increased and n(N)–p(Ge) π bonding is decreased upon κ²N metal coordination; a further weakening of the Ge–N bond occurs through triflate coordination to the Ge^II atom. Nevertheless, preliminary coordination studies revealed that 3 behaves as 2‐electron (L ‐type) germylene donor ligand. Treatment of 3 with [Ir(cod)Cl]₂ furnished the heterobimetallic complex [Rh(cod)(μ‐ 1 )Ge‐Ir(cod)Cl][OTf] ( 4 ), as evidenced by NMR spectroscopic investigations and DFT calculations.     

Electronic and Spatial Structure of Piperidine and Its Substituted Derivatives from the Results of ab initio Calculations

The results of non empirical quantum-chemical calculations using the RHF/6-31G(d) and MP2/6-31G(d) methods do not agree with proposals for the axial position of the H atom on the N atom in the piperidine molecule. According to RHF/6-31G(d) calculations for the N-methylpiperidine molecule and its chloro-substituted derivatives an equatorially placed methyl group is energetically more favored than an axial. The axial C-Cl and C-H bonds in these molecules are longer than the equatorial. The ³⁵ Cl NQR frequencies for the axial Cl atoms are lower than the equatorial. The ³⁵ Cl NQR frequency of the axial chlorine atom in 2-chloro-1-methylpiperidine is anomalously low. This is chiefly due to the high population density of its p σ-orbital and this is a result of the polarization of the C-Cl bond via the N atom unshared electron pair directly through the field. The effect of a similar unshared electron pair on the parameters of the C-Cl bond in the ClCH₂NH₂ molecule has been studied by the RHF/6-31(g) method for different angles of rotation of the ClCH₂ group around the C-N bond. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1044–1052, July, 2005.     

Unusual molecular structure of (C=O→Si←O′=C′) bis(2-methyl-4-pyrone-3-oxy)difluoro(λ6)siliconium

X-ray diffraction is used to determine the crystal and molecular structure of spirocyclic (C=O→Si←O′=C′) bis(2-methyl-4-pyrone-3-oxy)difluoro(λ⁶)siliconium containing a hypervalent silicon atom and the previously unknown F₂SiO₄ coordination center. The coordination polyhedron of the silicon atom is a slightly distorted octahedron.