The wavenumbers of the nu(3) metal-hydrogen stretching mode (T-1u) in the IR spectra of both ternary and quaternary hexahydrido salts of transition metals from groups 7 to 10 ([(MnH6)-H-I](5-), [(FeH6)-H-II](4-), [(RuH6)-H-II](4-), [(OsH6)-H-II](4-), [(IrH6)-H-III](3-), and [(PtH6)-H-IV](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.