Quantum‐Mechanical ab initio Investigation of the Transition‐Metal Compounds OsO₄, OsO₃F₂, OsO₂F₄, OsOF₆, and OsF₈

The equilibrium geometries of OsO 4 , OsO 3 F 2 , OsO 2 F 4 and OsF 8 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 OsO 4 has T d symmetry, for OsO 3 F 2 it has D 3 h symmetry, for OsO 2 F 4 C 2v symmetry with cis 1‐coordinated oxygen atoms, and for OsF 8 a D 2d symmetry with two different Os – F bond lengths is predicted. OsOF 6 is not a minimum on the potential energy hypersurface. The calculation of the thermodynamic stabilities indicates that the Os – F bond in OsF 8 is clearly weaker than in OsO 3 F 2 , OsO 2 F 4 and in OsF 6 . It will be very difficult to observe OsF 8 experimentally. The analysis of the electronic structure shows that the Os – O bond is partly covalent, while the Os – F bonds are mainly ionic.