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 (<i>R</i>² 0.95 with standard deviation 31 cm^–1) is found for the data with the equation ν_MH^calc = ν⁰ + Δν^<i>t</i> + Δν^<i>n</i>, where ν⁰ is the base wavenumber for the metal ion in question, Δν^<i>t</i> is the parameter of influence of the ligand <i>trans</i> to the hydride, and Δν^<i>n</i> is a correction for the charge of the complex [MHL₅]^<i>n</i>+. The introduction of a <i>cis</i> influence parameter has little effect on the correlation, showing that the <i>trans</i> 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.