Tungsten hexahydride (WH6). An equilibrium geometry far from octahedral

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Abstract
Ab initio all‐electron quantum mechanical methods were applied to the tungsten hexahydride (WH6) molecule using very large basis sets. Seven distinct structures were investigated with full geometry optimizations at the self‐consistent field (SCF) level of theory. The effects of electron correlation were estimated with second‐order Mo/ller–Plesset perturbation theory (MP2), modified coupled pair functional (MCPF) method, and the coupled cluster with single and double excitations (CCSD) method, and relativistic effects estimated using the Cowan–Griffin (mass–velocity and Darwin) corrections. Our results suggest that the ground state of the tungsten hexahydride (WH6) molecule is a closed‐shell triangular prism belonging to the C3v point group, with a set of three hydrogens stacked on top of another set of three hydrogens. From the perspective of inorganic chemistry, it is truly remarkable that the octahedral structure lies 130 kcal/mol above the C3v ground state. Furthermore, these results imply major qualitative differences between WH6 and the well‐known W(CH3)6 molecule. Another C3v structure, with one set of three hydrogens staggered with respect to the other set, is energetically nearby. With MCPF and relativistic corrections at the SCF optimized geometry, a third low‐lying structure belonging to the C5v point group is virtually degenerate with the triangular prism C3v structure.