Nickel nitrosyl (Ni-NO) complexes were studied by X-ray emission spectroscopy (XES) and density functional theory (DFT) to assess capabilities for XES to distinguish small molecule coordination modes and oxidation states. β-diketiminate Ni-NO complexes served as models for linear versus side-on NO coordination, and [NO]1-versus [NO]2-oxidation states in XES experiments. These NO coordination modes and oxidation states could all be experimentally distinguished by XES, offering an advantage over X-ray absorption spectroscopy (XAS). DFT calculations of the XES spectra with a simple one-electron model were in good agreement with experiment and allowed for orbital contributions to spectral features to be determined. For linear NO, the 2s2s σ* orbital transition had higher intensity than for side-on NO, while the 2s2s σ orbital had lower intensity. Fixing the Ni-N-O bond over the range from 80-176° evaluated the sensitivity of XES to NO coordination mode and suggested that XES could experimentally distinguish NO coordination angle differences of approximately 10°. This work highlights the ability for XES to quantify small molecule activation and NO coordination modes, and has implications for characterizing enzyme intermediates in NO and N2O reduction.

Quantifying nickel nitrosyl coordination modes with X-ray emission spectroscopy and computations

2019 Fall National Meeting

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