AB-INITIO SCF AND MOLLER-PLESSET STUDIES ON HEXAFLUORIDES OF SELENIUMAND TELLURIUM

SCF and Moller-Plesset calculations were done for the systems AB6 (TeF 6 and SeF6) and AB6E (TeF62- and SeF62-) to determine their relative s tabilities and geometric structures. The SCF calculations show that bo th TeF62- (as expected) and SeF62- (despite a small central atom) poss ess nonoctahedral shapes. However, at the Moller-Plesset level only th e TeF62- ion, studied with a large valence basis set, retains nonoctah edral geometry. The calculated structural parameters of the ion in C3v symmetry (the bond lengths are 2.212 and 1.975 angstrom and the bond angles are 104.9 and 83.4-degrees) differ considerably from the octahe dral values (2.101 angstrom and 90.0-degrees), yet the corresponding t otal energy is only about 1 kcal/mol smaller. The results show signifi cant dependence of the computational predictions on the basis sets use d and indicate the need to include electron correlation effects in the studies devoted to establishing the stereochemical activity of the lo ne electron pair. (C) 1993 by John Wiley & Sons, Inc.