Nickel(II)-polypyridine complexes: bridging XPS insights with DFT calculations

The electrochemical oxidation of a series of tris(polypyridine)nickel(II) complexes ( 1–8 ) yields Ni(III) species with oxidation potentials ( E 1/2 ) showing a direct correlation to the Ni 2p 3/2 binding energy (BE) determined by XPS. Higher oxidation potential correspond to increased binding energies, indicating a consistent relationship between electrochemical and spectroscopic descriptors of the nickel centre. Spin-orbit splitting (ΔBE 1 ) increased with electron deficiency, while satellite shake-up features (ΔBE 2 ) and satellite intensity ratio ( i ratio ) reflect variations in the ligand-metal covalency and charge transfer behaviour. Distinct trends are observed between bipyridine- and 1,10-phenanthroline-based complexes, highlighting the influence of the ligand structure. DFT-calculated core-level energies, highest occupied molecular orbital (HOMO) energies, ionization potentials, and electronegativity parameters show strong agreement with experimental X-ray Photoelectron Spectroscopy (XPS) data, supporting the observed electronic structure, and XPS signatures in Ni(II) polypyridine systems.