NQR studies of intramolecular complexes in organic compounds of metals of group IVA

2012

Chem Heterocycl Comp

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.

supporting

confidence: 74%

mentioning

confidence: 99%

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

2012

Chem Heterocycl Comp

“…In its 35 Cl NQR triplet spectrum (Feshin et al, 1984), one line is shifted to an appreciably lower frequency diapason (21.028 MHz) as compared with two others (23.139 and 24.040 MHz). As in other chlorine-containing molecules of trigonal-bipyramidal structure, the Ge-Cl axial bond in this molecule (2.181 Å ) is appreciably longer than two equatorial bonds (2.138 and 2.144 Å ) (Feshin et al, 1984;Gurkova et al, 1984), and the NQR frequency of its Cl atom is considerably lower than the NQR frequencies of equatorial Cl atoms (Feshin et al, 1984;Feshin and Polygalova, 1991).…”

Section: Introductionmentioning

confidence: 53%

“…Some of the said compounds have been investigated by X-ray diffraction (Gar et al, 1982;Feshin et al, 1984Feshin et al, , 1989Gurkova et al, 1984aGurkova et al, , b, 1985Shipov et al, 2011), by nuclear quadrupole resonance (NQR) on the 35 Cl nuclei (Gar et al, 1982;Feshin et al, 1984Feshin et al, , 1989Feshin et al, , 1991, and by nonempirical methods of quantum chemistry (e.g., Feshin andFeshina, 2010, 2011).…”

Section: Introductionmentioning

confidence: 99%

Structure and 35Cl NQR parameters of 1,3-diphenyl-3-methyl-3-(trichlorogermyl)butanone-1 using ab initio calculations

Main Group Metal Chemistry

2012

Quantum-chemical calculations at the RHF/6-31G(d) and MP2/6-31G(d) levels of two stable structures of 1,3-diphenyl-3-methyl-3-(trichlorogermyl)butanone-1 molecule were executed. According to calculations at the RHF/6-31G(d) level, the structure with pentacoordinated Ge atom is by 7.49 kJ/mol energetically more advantageous as compared with that with the tetracoordinated one. Using 3 p -components of the Cl atom valence p -orbitals obtained from these calculations, the 35 Cl nuclear quadrupole resonance (NQR) parameters of this compound with the pentacoordinated Ge atom were assessed. Calculations performed at both the RHF/6-31G(d) and MP2/6-31G(d) levels do not differ principally and are close to experimental NQR data. Calculations at the RHF/6-31G(d) level performed at various Ge ‧ ‧ ‧ O distances demonstrated that convergence of the Ge and O coordination centers leads to an increase in the positive charge at the Ge atom and in the negative charge at the O atom, and with that, electron density from the Ge atom shifts mainly to the axial Cl atom and from the C atom of carbonyl group to its O atom. On such convergence, the electron density of atoms directly bonded to those of the Ge coordination polyhedron decreases to some extent.

“…Unfortunately, the asymmetry parameters of the electric field gradient (EFG) at the nuclei 35 Cl of these compounds were not measured. DOI: 10.1134/S1070363212050088 Typically, in the case of significant intramolecular interaction of an atom of the element of Group IVA with the heteroatom of the carbofunctional substituent a 5-or 6-membered ring is closed [2][3][4]. In the 2-alkoxyphenyltrichlorostannane such interaction would lead to the closure of 4-membered ring.…”

mentioning

confidence: 99%

Stereoelectronic structure of methoxyphenyltrichlorostannanes by the results of ab initio calculations

2012

Russ J Gen Chem

The RHF/3-21G* and MP2/3-21G* levels were implemented for the study of the stereoelectronic structure of 2-and 4-methoxyphenyl-and 2,6-dimethoxyphenyltrichlorostannanes. In the 4-methoxyphenyltrichlorostannane the Sn atom is tetracoordinated, while in 2-methoxy-and 2,6-dimethoxyphenyltrichlorostannanes it is pentacoordinated due to the intramolecular interaction of the O atom with it. In this case a closure occurs of a 4-membered ring. In the last molecule, the Sn atom interacts almost exclusively with only one of the O atoms. The intramolecular interaction between the Sn and O atoms leads to the electron density transfer from C and H atoms of the methoxy groups as well as from the Sn atom to the atoms of its coordination polyhedron. As a result the electron density increases also on the O atom involved in this interaction.Investigation of 2-methoxyphenyltrichlorostannane by nuclear quadrupole resonance (NQR) on the 35 Cl nuclei has shown [1] that the Sn atom can be pentacoordinated through additional interaction with the oxygen atom of the methoxy group. For example, in the triplet 35 Cl NQR spectrum of 2-CH 3 OC 6 H 4 SnCl 3 at 77 K the low-frequency line (20.070 MHz) is considerably removed from the high-frequency doublet (21.762 and 21.674 MHz). The expansion of the Sn atom coordination in such compounds may result in either intra-or intermolecular interaction of the Sn and O atoms. In the NQR spectrum of 4-CH 3 OC 6 H 4 SnCl 3 which is incapable of such intramolecular interaction the splitting of the lines is relatively small (21.299, 21.204, 21.160, 21.008, 20.728 and 20.385 MHz). Apparently, the unit cell of this compound contains two crystallographically nonequivalent molecules. The relatively narrow range of frequencies of this spectrum and a small splitting of its lines indicate that the difference in the electron distribution of the chlorine atoms of this compound is insignificant. This allows us to conclude that the Sn atom is tetracoordinated and a significant intermolecular Sn←O interaction does not occur. Unfortunately, the asymmetry parameters of the electric field gradient (EFG) at the nuclei 35 Cl of these compounds were not measured.