Unusual sevenfold coordination of Ru in complex hydride Na3RuH7: Prospect for formation of [FeH7]3– anion

We used density-functional calculations to clarify the origin of the unusual sevenfold coordination of Ru by H in Na3RuH7. We found that the D5h symmetry of the ligands enables the formation of strong covalent bonds of Ru and H through ligand-field effects, stabilizing the sevenfold coordination. We also examined the possible synthesis of the hypothetical 3d analog, Li3FeH7, which has a gravimetric hydrogen density of 8.4 mass%. The calculated enthalpy change of −16 kJ/mol H2 for the reaction, 3LiH+Fe+2H2→Li3FeH7, reveals a possible route to a stable complex hydride containing [FeH7]3–.