Ab initio study of the structure, force fields, and vibrational spectra of alkali metal tellurites

Abstract

The equilibrium geometrical parameters, force fields, vibration frequencies, and intensities in the IR molecular spectra of M₂TeO₃ (M-Li, Na, K) are found by the Hartree — Fock ab initio method in the bases complemented with polarization and diffusion functions using relativistic effective core potentials. The relative energies of alternative molecular configurations and the energies of the dissociation M₂TeO₃→ M2O + TeO2 are refined using Möller — Plessett second-order perturbation theory. It is found that the chemical bond in these molecules can be approximated by the scheme (M⁺)₂[TeO₃]^2- The equilibrium nuclear configuration has C_s symmetry and corresponds to the bis-bidentate coordination of M₊ cations by the pyramidal anion [TeO₃]^2-. The mono-bidentate structures of C_s symmetry correspond to the saddle points on the potential energy surface of the molecules. The calculated IR molecular spectrum of K₂TeO₃ agrees with the experimental spectrum obtained by the matrix isolation method by J. Ogden et al. [J. Chem. Soc. Dalton Trans., 1957 (1997)]. Based on the results of the previous ab initio studies of alkali metal sulfites and selenites, the barrier of the intramolecular rearrangement (bb)→(mb)→(bb)’ was found to lower in the series Li₂XO₃→Na₂XO₂→K₂XO₃ (X = S, Se, Te) and M₂TeO₃→M₂SeO₃→M₂SO₃. The degree of deformation of the XO fragment in the M₂XO₃ molecules decreases when the M atom is replaced by its heavier analog (Li→Na→K).