Quantifying the Interdependence of Metal–Ligand Covalency and Bond Distance Using Ligand K-edge XAS

Abstract

Bond distance is a common structural metric used to assess changes in metal–ligand bonds, but it is not clear how sensitive changes in bond distances are with respect to changes in metal–ligand covalency. Here we report ligand K-edge XAS studies on Ni and Pd complexes containing different phosphorus(III) ligands. Despite the large number of electronic and structural permutations, P K-edge pre-edge peak intensities reveal a remarkable correlation that spectroscopically quantifies the linear interdependence of covalent M−P σ bonding and bond distance. Cl K-edge studies conducted on many of the same Ni and Pd compounds revealed a poor correlation between M−Cl bond distance and covalency, but a strong correlation was established by analyzing Cl K-edge data for Ti complexes with a wider range of Ti−Cl bond distances. Together these results establish a quantitative framework to begin making more accurate assessments of metal–ligand covalency using bond distances from readily-available crystallographic data.