V. P. Feshin

Correlation between the 35CI NQR Parameters of Chloro-containing Organic and Organometallic Compounds and the Results of ab initio Calculations

Abstract The results of comparison of experimental 35C1 NQR parameters for a great number of organic and organometallic compounds and estimated ones using ab initio calculations at the RHF/6-31G(d) level were systematized. The NQR frequency changes on going from one compound to another depend, in general, on the changes of populations of the CI atom po-orbitals in these compounds and, first of all, of populations of their less diffuse parts

Spatial electron density distribution of the chlorine atoms in organic and complex compounds as studied by NQR and MNDO

Abstract Quantitative correlation of the NQR frequencies and asymmetry parameters of the EFG at nuclei having spin I = 3 2 with the population of the indicator atom (at N p x = 2) and nonaxiality of its electron distribution has been obtained. The N p y and N p z populations of the Cl atoms in some chloro-containing organic and coordination compounds have been calculated using the obtained equations. These populations have been compared with those found from MNDO calculations. Taking into account the results obtained, the peculiarities of electron distribution in substituted chloroethylenes, carbon acid chloroanhydrides, chlorophosphoranes and MCl 4 complexes (M = Si, Ge and Sn) have been analyzed.

Ab initio and MNDO Calculations of the 35Cl NQR Parameters of Some Organic and Inorganic Molecules

Abstract The results of ab initio and MNDO calculations of the Cl2C = CHOCH3 , XCOCl (X = CH3 , OCH3 and COCl), 4-ClC6H4CH2Cl, (CNCl)3 and PCl5 with total optimization of their geometry are presented. The ab initio calculations were executed using Hartree-Fock theory and the split valence basis set 6-31G* (RHF/6-31 G*//RHF/6-31G*). Using the calculated p-orbital populations of the CI atoms in these molecules the 35Cl NQR frequencies and asymmetry parameters of the EFG at the 35Cl nuclei have been determined. When the populations of the less diffuse components of orbitals in the split valence basis set are used the calculated and experimenal ν and η values are in good agreement. Linear correlations between these calculated and corresponding experimental ν and η values are obtained. The causes of the nonconformity of the earlier calculated ν and η values and their experimental ones are analysed.

p, π-interaction in the group using the NQR technique and MNDO calculations

Abstract The experimental EFG asymmetry parameters at the halogen nuclei in molecules containing the group do not corroborate widespread representations of a p, π-conjugation between the unshared electron pair of the halogen atom and the π-electron double bond system in these molecules. MNDO calculations of ethylene and its derivatives and analysis of p x -orbital populations of the C and Y atoms in the group of these molecules conform to the experimental data in question. These calculations as well as those of XCH=CH 2 (X=F, Cl and CH 3 ) molecules with varying CX bond lengths, and systems XCH=Ch 2 −HF and [XCH=CH 2 ] 1+ − HF with varying distance between the system fragments, conform to an electrostatic mechanism of p x -electron density distribution in such molecules.

Ab initio and MNDO Calculations of Cyanuric Chloride, its 35Cl NQR Frequency and Asymmetry Parameter of the EFG at the 35Cl Nuclei

Ab initio molecular orbital calculations of the (CNCl)3 (cyanuric chloride; 2,4,6‐trichloro‐1,3,5‐triazine) molecule were performed at the RHF/6–31G* level. The 35Cl NQR frequency and asymmetry parameter of the EFG at the 35Cl nucleus were calculated from the total populations of the Cl atom valence p‐orbitals and their components. The 35Cl NQR frequency and asymmetry parameter which are determined for (CNCl)3 based on these components agree well with the corresponding experimental values and demonstrate the importance of including the less diffuse components of the p‐orbitals.

Nature of coordination bond in silatranes and its formation dynamics according to the ab initio calculations

Quantum-chemical calculations of 1-hydrosilatrane molecule with complete optimization of its geometry and at various fixed Si…N distances (2.0 to 3.7 Å) has been carried out at the MP2/6-31G(d) level. The silatranes coordination bond is formed of different atomic orbitals of Si and N atoms participating in a series of molecular orbitals. With the Si…N distance decreasing, contributions of the atomic orbitals in these molecular orbitals have been changed, number of the molecular orbitals has increased, and total energy of the molecule has decreased. At the coordination centers are getting closer, population of the nitrogen valence s and pz orbitals have changed due to the corresponding bond angle change; the populations of Si and H orbitals are not significantly changed.

Peculiarities of atomic interaction in organic molecules of 3- and 4-coordinated phosphorus using ab initio calculations and 35Cl NQR

Abstract The results of ab initio calculations at the MP2/6-31G(d) level of molecules of the series ClPXX′ (X, X′=C 2 H 5 , N(CH 3 ) 2 , OCH 3 ) and ClP(M)XX′ (M=O, S; X=CH 3 , ?CH 3 ; X′=C 2 H 5 , OCH 3 ) with total optimization of their geometry were presented. They were compared with the obtained earlier results of such calculations at the RHF/6-31G(d) level and with experimental 35 Cl nuclear quadrupole resonance (NQR) spectra for these compounds. MP2/6-31G(d) calculations confirm non-inductive influence of heteroatoms on the geminal Cl atom in the non-linear three-atomic Cl–P–M groups. They agree to the conclusion that the abnormal correlation of the 35 Cl NQR frequencies for the compounds studied at different X, X′ and M is caused, in general, by the P–Cl bond polarization under the action of the geminal atom partial charges directly through the field. The satisfactory conformity between the experimental 35 Cl NQR frequencies and those estimated from 3p-components of the Cl atom valence p-orbitals calculated at the MP2/6-31G(d) level was obtained.

Peculiarities of atomic interaction in molecules ClP(M)(OCH3)2 (M = O and S) using ab initio calculations

Abstract The results of ab initio calculations at the RHF/6-31G* level of the ClP(M)(OCH 3 ) 2 (M = O and S) molecules were presented. They were used for the interpretation of abnormal influence of the M atom and of the O atoms in methoxy group on C1 and, in particular, of abnormally low 35 Cl NQR frequencies for these compounds, as well as of abnormal correlation between their NQR frequencies at M = O and S. It is shown, that these anomalies are caused by peculiarities of p-electron density distribution of Cl atoms in these molecules, as well as in other molecules containing non-linear three-atomic group Cl–Z–M.

MNDO STUDIES OF THE SiCI4 COMPLEXES WITH SOME ORGANIC LIGANDS

MNDO calculations of the S1CI4 complexes with pyridine, trimethylamine and tetramethyl urea have been carried out when the coordinate of the reaction of complex formation is varied. These calculations conform to the experimentally established structure of these complexes. The changes of atomic charges and p-orbital populations of atoms at decrease of the distance between the complex components have been analysed. The peculiarities and mechanism of formation of complexes of different structures have been examined.

35Cl NQR Spectra of SnCl4 Complexes with Methylaryl Ethers

SnCl4 Complexes with methylaryl ethers and their 35Cl NQR spectra have been obtained. All these complexes, except SnCl4 · 1,2-(CH3O)2C6H4, have a trigonal-bipyramidal structure. The latter compound has an essentially distorted octahedral structure. One of the ligand oxygen atoms takes part in the formation of the SnCl4 complex with 1,3-, 1,4-(CH3O)2C6H4 and RNO2. These complexes have a trigonal-bipyramidal structure too.