Ni 2p–3d photoabsorption and strong charge transfer satellites in divalent Ni complexes with molecular ligands. Evaluation of π-back donation based on the density functional theory approach

Density functional theory within a transition potential approach (DFT-TP) is applied to interpret remarkably strong π-type MLCT (metal-to-ligand charge transfer) satellites in the Ni 2p photoabsorption of planar low-spin NiII complexes, K2Ni(CN)4·H2O and bis(dimethylglyoximato)nickel. The MLCT intensities calculated with DFT-TP are in good agreement with experiment, whereas the HF-STEX (Hartree–Fock-based static exchange approximation) approach underestimates the intensities. The DFT-TP approach gives more reasonable π-back donation due to a better description of the strong covalency hybridization of the ligand π* orbitals with the occupied 3d orbitals. The DFT analysis indicates that we can evaluate π-back donation qualitatively by experimentally examining the MLCT satellites.