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Relationship between Transition-Metal Hydride Bond Lengths and Stretching Wavenumbers
1Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario M5S-3H6, Canada.
Abstract:
Here it is demonstrated that there is a linear relationship between the terminal 3d metal hydride stretching wavenumber νMH and the metal hydride distance dMH reported to date: νMH ∼ (-1.05dMH + 3.35) × 103 cm-1. That is, upon moving from Group 3 to Group 10 metals in complexes and binary molecules, νMH (cm-1) increases as the metal-hydrogen distance dMH (Å) decreases as determined by X-ray diffraction, molecular spectroscopy, and, in one case, neutron diffraction. This trend contrasts with the relatively constant bond dissociation free energy (BDFE) of the diamagnetic complexes and the usually smaller BDFE (by as much as -20 kcal/mol) of paramagnetic ones, thus showing that there is no correlation between either νMH or its force constant with the BDFE. If a positive charge is added to the complex by metal-ion oxidation, νMH may increase or decrease depending on the coordination number and spin state of the complex.
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