On the problem of the vibrational frequencies of water in complexes

Abstract

An attempt has been made to calculate the vibrational frequencies of water in aquocomplexes, with particular regard to the shifts of the frequencies of the fundamental vibrations of the free water molecule. On the basis of the electrostatic model of a coordination molecule of the type MeH 2 O, two different types of calculations has been carried out: 1) A potential function of the Van Vleck-Cross type (J. Chem. Phys., 1, 1933, 357) with additional terms corresponding to the electrostatic interactions between the metal ion and the coordinated water molecule has been developed in series of powers of the internal coordinates in order to obtaine equilibrium positions and values of the force constants; these numerical values have been used to solve the vibrational problem by the usual method of the F, G matrices. 2) A perturbation method with the eigenfunctions of the normal vibrations of the free water molecule as unperturbed wave functions and the operator of the electrostatic interaction metal-water as the perturbation operator has been also used. Both types of calculations have led to the prevision that the two stretching frequencies of water are lowered in the aquocomplexes by an amount of the order of 3–400 cm −3, while the bending frequency is raised by few tens of cm −1. Both expectations agree very well with the experimental data.