Counterion Influence on the Vibrational Wavenumbers in Ternary and Quaternary Metal Hydride Salts, A2MH6 (A = Alkali Metal, Alkaline Earth, and Lanthanides; M = Ir, Fe, Ru, Os, Pt, Mn)

The wavenumbers of the ν3 metal–hydrogen stretching mode (T1u) in the IR spectra of both ternary and quaternary hexahydrido salts of transition metals from groups 7 to 10 ([MnIH6]5–, [FeIIH6]4–, [RuIIH6]4–, [OsIIH6]4–, [IrIIIH6]3–, and [PtIVH6]2–) depend linearly upon the ionization energies of the counterions (alkali metal, alkaline earth, and lanthanide) with a separate line for each metal. This relationship provides quantitative support for the charge-transfer mechanism for explaining the stabilities of these compounds.