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Updated: Jun 4, 2025

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Published on: July 27, 2022
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.
A linear relationship exists between metal hydride bond length and stretching frequency in 3d transition metals. This finding reveals no correlation with bond dissociation free energy, offering new insights into metal-hydride chemistry.
Area of Science:
- Inorganic Chemistry
- Materials Science
- Spectroscopy
Background:
- Metal hydrides are crucial in catalysis and materials science.
- Understanding the metal-hydrogen bond is key to predicting reactivity.
- Existing data on metal hydride properties is extensive but lacks a unifying trend.
Purpose of the Study:
- To establish a quantitative relationship between metal hydride bond length and vibrational frequency.
- To investigate the correlation between vibrational properties and bond dissociation free energy (BDFE).
- To explore the impact of metal oxidation state on metal-hydride vibrational characteristics.
Main Methods:
- Analysis of published X-ray diffraction and molecular spectroscopy data for 3d metal hydride complexes and molecules.
- Inclusion of one neutron diffraction dataset for validation.
- Correlation analysis between metal-hydride distance (d_MH) and stretching wavenumber (ν_MH).
- Comparison of vibrational data with reported BDFE values for diamagnetic and paramagnetic complexes.
Main Results:
- A clear inverse linear relationship was identified: ν_MH (cm⁻¹) ≈ (-1.05 * d_MH + 3.35) * 10³.
- Metal hydride stretching frequency increases as the metal-hydrogen bond distance decreases across Groups 3-10.
- No correlation was found between ν_MH or its force constant and the BDFE.
- Metal ion oxidation can lead to variable changes in ν_MH, dependent on coordination number and spin state.
Conclusions:
- The established linear trend provides a predictive tool for metal-hydride vibrational properties based on bond length.
- Vibrational frequency is not a reliable indicator of metal-hydride bond strength (BDFE).
- Oxidation state significantly influences metal-hydride vibrational behavior in a complex manner.
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