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

摘要

Density functional theory within a transition potential approach (DFT-TP) is applied to interpret remarkably strong #pi#-type MLCT (metal-to-ligand charge transfer )satellites in the Ni 2p photoabsorption of planar low-spin Ni~(II) complexes, K_2Ni(CN)_4 centre dot H_2O 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 #pi#-back donation due to a better description of the strong covalency hybridization of the ligand #pi#~* orbitals with the occupied 3d orbitals. The DFT analysis indicates that we can evaluate #pi#-back donation qualitatively by experimentally examining the MLCT satellites.