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

Abstract

RHF/6-31G(d) and 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. 35 Cl 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.Keywords: 1-(1-trichlorogermylethyl)pyrrolidin-2-one, coordination interaction, germanium atom coordination polyhedron, p-orbital populations, quantum-chemical calculations, RHF/6-31G(d) and MP2/6-31(d) calculations, stereoelectronic structure, valence p-orbitals.In organic trichlorogermanium compounds, the germanium atom may participate in an intramolecular interaction with a heteroatom of the organic substituent, thereby increasing its coordination number to five. This usually results in closure of a five-membered ring. Some of these compounds have been studied by X-ray diffraction structural analysis (XSA) [1-3] and 35 Cl nuclear quadrupole resonance (NQR) [3][4][5][6]. The stereoelectronic structure of some of these compounds and the nature of the coordination bond have been studied by nonempirical quantum-chemical calculations [7][8][9].In a continuation of this investigation, we carried out RHF/6-31G(d) and MP2/6-31(d) calculations using the Gaussian 03W program [10] for the stereoelectronic structure of 1-(1-trichlorogermylethyl)pyrrolidin-2-one molecule. This molecule is known in form 1 with a pentacoordinated germanium atom and has both XSA and 35 Cl NQR data, which may be compared with the calculation results. We have analysed the changes in the electron distribution in this molecule upon the formation of the Ge←O coordination bond, evaluated the 35 Cl NQR frequencies and asymmetry parameters of the electric field gradient (EFG) on the 35 Cl nuclei of this _______ *Dedicated to Academician M. G. Voronkov on his 90th birthday.