Electronic and Steric Structure of ClAsX2 Molecules: Evaluation by 35Cl NQR and Quantum-Chemical Calculations

Abstract

Molecules of the series ClAsX 2 [X = C 2 H 5 , N(CH 3 ) 2 , OCH 3 ] were studied by RHF/6-31G(d) and MP2/6-31G(d) calculations. Their 35 Cl NQR frequencies were calculated from the populations of the 3p constituents of the chlorine valence p orbitals. The features of interaction of the geminal atoms in the molecules and the effect of this interaction on the electron distribution in them were analyzed.We attained reasonable agreement between the experimental 35 Cl NQR frequencies n of chlorinecontaining organic and organometallic compounds and those calculated by the equation given below [1] from the populations of the 3p constituents of the chlorine valence p orbitals, which, in turn, were found by various methods of ab initio quantum-chemical calculations (see, e.g., [23 4]).Here e 2 Qq at is the atomic quadrupole interaction constant; h, Planck constant; h, asymmetry parameter of the electric field gradient at the nucleus of the resonating atom with the nuclear spin I = 3/2; and N x , N y , and N z , populations of the valence p x , p y , and p z orbitals of the indicator atom, respectively. This agreement allows more comprehensive interpretation of the experimental 35 Cl NQR spectra using the results of quantum-chemical calculations, estimation and discussion of the 35 Cl NQR frequencies of compounds for which it is impossible to measure the NQR spectra, etc. By this integrated method ( 35 Cl NQR and quantum chemistry), we studied the electronic and steric structure of a large number of organic and organometallic molecules and the features of the mutual influence of atoms in them. In particular, we studied compounds containing ClZM (Z = C, Si, P) and ClZ=M (Z = C, P) groups in which the effect of the heteroatom M on the Cl atom does not correspond to its electronegativity and to the inductive effect of the M-containing substituent [2, 539]. Proceeding with these studies, we made here the quantum-chemical calculations [RHF/6-31G(d), MP2/6-31G(d)] of ClAsX 2 molecules [X = C 2 H 5 (I), N(CH 3 ) 2 (II), OCH 3 (III)] with full optimization of their geometry. The calculations were performed using the GAUSSIAN-94W program [10]. The coordinate system was chosen so that the origin coincided with the Cl nucleus and the Z-axis was directed along the Cl3As bond.