Ternary Group VIII Hydrides: Ligand Field and Cation Orbital Effects in their Electronic Structures

The electronic structure and bonding of some recently discovered ternary hydrides with group VI11 metals are evaluated using tight-binding extended Hiickel band structure calculations. Various computational tools that include charge iteration of the transition metal orbital parameters, Mulliken population analyses, and second moment scaling methods were utilized to examine the bonding in Mg2RuH4 and MgpRuH3. Our results indicate that the unusual sawhorse geometry of the d8 RuH4 fragment in MgzRuH4 is preferred over a square planar configuration due to zeroth-order ligand field effects, oxidation state at the transition metal, and metal-metal bonding between adjacent fragments. In the extraordinary structure of Mg3RuH3, Mg valence orbitals are actively involved in chemical bonding and contribute to the stability of the unusual electron count at Ru