Electronic structure and photoelectron spectra of nickel (II) acetylacetonate and its thio- and amino-substituted analogues

Using ultraviolet photoelectron spectroscopy and electron density functional theory (DFT), we investigated the electronic structure of the d8 complex acetylacetonate Ni(a≿а≿)2 and its NH, S and NCH2-substitutes: nickel bis(acetylacetoneiminate) (Ni(acim)2), Ni(Sacac)2 and nickel N,N′-Ethylene-bis(acetylacetoneiminate) (NiEcim), respectively. Based on the spectral regularities and calculated results for these four compounds, we interpreted the PE spectra to approximate the extended Koopmans' theorem IEi = -εi + δi using the δi relationship to the molecular orbital type, which differs substantially from earlier published interpretations. We determined the vertical ionization energies for the four pairs of ligand n- and π-levels and four d-type orbitals for the metal. We further discussed the regularities established both experimentally and theoretically for the influence that substituting S, NH and NCH2- for O exerted on the electronic and spatial structure of the complexes, effective atomic charges and intra-complex coordinate bonds.