Nickel(II) chromophores with the 2,6-bis(diphenylphosphinomethyl)pyridine ligand: XPS characterization of the electronic structure

XPS data are reported for Ni, N, P and L atoms (L = ligand Cl-, NO3-, ClO4-, NCS-) in the chromophores of Ni/(PNP) complexes (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine ligand), and the structural implications are discussed. Quadratic [Ni(PNP)L] chromophores are well characterized through low Ni2p binding energy values and covalent XPS patterns of L ligands. Ni(PNP)(NCS)2 reveals a well defined presence of [Ni(PNP)(NCS)] quadratic chromophores, as well as of more ionic NCS- ligands, possibly contained in pseudooctahedral [Ni(PNP)(NCS)3]- environments as suggested by previous investigations. Definite evidence is presented for the occurrence of 2 inequivalent (PNP) ligands in cationic [Ni(PNP)2]2+ species, 1 terdentate with bonded N, and 1 bidentate with noncoordinated pyridine N.