QUANTUM-MECHANICAL ABINITIO INVESTIGATION OF THE TRANSITION-METAL COMPOUNDS OSO4, OSO3F2, OSO2F4, OSOF6, AND OSF8

The equilibrium geometries of OsO4, OsO3F2, OsO2F4 and OsF8 are theoretically predicted by using quantum-mechanical ab initio methods at the Hartree-Fock and MP2 level of theory employing quasi-relativistic pseudopotentials for Os and 3-21G and 6-31G(d) basis sets for O and F. A comparison of the calculated geometries and vibrational frequencies with available experimental results shows a good agreement. The energy minimum structure for OsO4 has T(d) symmetry, for OsO3F2 it has D3h symmetry, for OsO2F4 C2v symmetry with cis-coordinated oxygen atoms, and for OsF8 a D2d symmetry with two different Os - F bond lengths is predicted. OsOF6 is not a minimum on the potential energy hypersurface. The calculation of the thermodynamic stabilities indicates that the Os - F bond in OsF8 is clearly weaker than in OsO3F2, OsO2F4 and in OsF6. It will be very difficult to observe OsF8 experimentally. The analysis of the electronic structure shows that the Os - O bond is partly covalent, while the Os - F bonds are mainly ionic.