Strong metal-to-ligand charge transfer bands in Ni 2p photoabsorption of K2Ni(CN)4·H2O

Polarized Ni 2p photoabsorption spectra were measured for a single crystal of planar (D4h) NiII complex with low-spin 3d8 configuration, K2Ni(CN)4·H2O, in comparison with powder spectra of CaNi(CN)4 and BaNi(CN)4. Remarkably strong satellite bands are found besides the lowest Ni 2p–3d* atomic lines. Two features in the satellite show different polarization dependencies, and are assigned to the metal-to-ligand charge transfer (MLCT) transitions to out-of-plane eg π* and in-plane b2g π* ligand orbitals, respectively, in good agreement with ab initio molecular orbital predictions. The low-lying ligand π* orbital is essential in the metal 2p photoabsorption of 3d transition metal compounds with strong π backbonding.