Quantum‐Mechanical ab initio 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 D_3h symmetry, for OsO₂F₄ C_2v symmetry with cis1‐coordinated oxygen atoms, and for OsF₈ a D_2d 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.