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Nickel K-Edge XANES Studies on Pyridinophane-Supported Coordination Complexes
Luke P Westawker1, Rachel F Wallick1, Jason W Schultz2
1Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois61801, United States.
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X-ray absorption spectroscopy (XAS) is a powerful technique to identify the electronic and geometric structures surrounding a specific element and is of growing interest for the characterization of homogeneous organometallic compounds, especially for sensitive and highly reactive in situ species. In this study, we performed a systematic, quantitative analysis of the rising Ni K-edge for a series of 25 pyridinophane-supported compounds by fitting the K-edge to the relevant 1s to 4p transitions. We observe how ligand substitution, the oxidation state, and variable binding modes have a direct effect on the energy and shape of the Ni K-edge as they affect Ni bond distances and p-orbital symmetry. By leveraging the flexible denticity of pyridinophane ligands, we quantify the variable solution-phase binding mode of previously ambiguous structures. This study also helps establish using the intense, rising Ni K-edge to monitor in situ reactivity and to characterize coordination environments of Ni catalysts using only 1-2 scans, without relying on the EXAFS region.
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