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

The results of ab initio calculations at the MP2/6-31G(d) level of molecules of the series ClPXX′ (X, X′=C₂H₅, N(CH₃)₂, OCH₃) and ClP(M)XX′ (M=O, S; X=CH₃, ?CH₃; X′=C₂H₅, OCH₃) 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 ³⁵Cl 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 ³⁵Cl 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 ³⁵Cl 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.