Estimating the Wavenumber of Terminal Metal-Hydride Stretching Vibrations of Octahedral d⁶ Transition Metal Complexes

The wavenumbers of 774 terminal hydride infrared active stretching modes of 478 distinct classes of structures of d⁶ octahedral complexes of Mn­(I), Re­(I), Fe­(II), Ru­(II), Os­(II), Co­(III), Rh­(III), Ir­(III), and Pt­(IV) were collected from the literature. A fair correlation (R² 0.95 with standard deviation 31 cm^–1) is found for the data with the equation ν_MH^calc = ν⁰ + Δν^t + Δνⁿ, where ν⁰ is the base wavenumber for the metal ion in question, Δν^t is the parameter of influence of the ligand trans to the hydride, and Δνⁿ is a correction for the charge of the complex [MHL₅]ⁿ⁺. The introduction of a cis influence parameter has little effect on the correlation, showing that the trans influence dominates in this case. The equation is useful in identifying anomalous data reported in the literature, validating future assignments of ν_MH, understanding better metal-hydride bonding, and possibly assisting in identifying superior hydride-based catalysts.