Ab initio calculations on some transition metal heptoxides by using effective core potentials

Abstract

The ab initio molecular structures and vibrational frequencies for several transition metal heptoxides X 2 O 7 nϪ (n 0, 2, 4) were calculated using effective core potentials at the HF and DFT (B3LYP) levels. The relative merits of different valence basis set arrangements were tested by comparison with experimental results available, in particular with gas-phase Re 2 O 7 molecular structure and vibrational frequencies. The calculations were then extended to other heptoxides of the VB, VIB and VIIB transition metal groups. The results indicate that a staggered geometry (either D 3d or C 2 ) is the energy minimum for most of the heptoxides studied. The only exceptions are Mn 2 O 7 , which clearly prefers an eclipsed C 2v(syn) configuration, and Tc 2 O 7 , for which C 2 and C 2v(syn) geometries have nearly the same energy.Particular attention was given to the magnitude of the X-O-X bond angle, as this structural parameter has been a matter of some controversy. The calculated values range from 125Њ (Mn 2 O 7 ) to 180Њ (Group VB heptoxides) and depend on the position of the transition metal in the Periodic Table. A tendency for linearity of the X-O-X moiety on going both downwards the group and backwards the period was observed and discussed. ᭧

Effective core potential ab initio calculations on main group heptoxides and large silicate systems

“…A general good agreement between the calculated and the reported experimental values, for both structural parameters and vibrational frequencies, was found by using the therein-selected ECP combination [1]. The overall results showed a clear tendency to linearity of the X-O-X framework on going both downwards a group and backwards a period VIIB 3 VB; with the VB heptoxides presenting a perfectly centrosymmetric molecular geometry.…”

“…In a recent publication [1] we have reported the calculated ab initio molecular structures and vibrational frequencies for the heptoxides of the VB, VIB and VIIB transition metal groups (general formula X 2 O nϪ 7 , see Scheme 1 below), by using effective core potentials (ECP) at both HF and B3LYP levels. The relative energies of all optimized configurations, as well as the particular conformational preferences of each heptoxide, were presented and discussed.…”

“…The relative energies of all optimized configurations, as well as the particular conformational preferences of each heptoxide, were presented and discussed. Special emphasis was given to the magnitude of the X-O-X bond angle, as it raised some attention in the last few years [1][2][3][4][5][6][7][8][9][10][11][12][13].…”

Structure of barium chloride-oxide tellurite glasses

“…As shown in Refs. [31,32], such choice of bases leads to good results for systems similar to one under consideration. Standard 3-21G basis was used for hydrogen atoms.…”

On the structure of tungstate–tellurite glasses

“…As shown in Refs. [24,25], such a choice of the basis provided a good description of properties of the systems similar to those under consideration. Standard 3-21G basis set was used for hydrogen atoms.…”