Determination of the electronic structure in the strongly correlated 1-D electron systems: X-ray photoelectron and auger spectroscopy of halogen-bridged nickel complexes

The electronic structure of the 1-D Ni complexes, [Ni(chxn)₂X]X₂ (X=Br, Cl) is studied together with the discrete Ni complexes, [NiX₂([14]aneN₄)]C1O₄(X=Br, Cl), using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). An analysis using a simple X-Ni-X trimer model on the Ni 2p XP spectra yields quantitative estimates for the charge transfer (CT) energy Δ and the transfer energy T. An analysis on the Ni LVV Auger spectra indicates that the average on-site Coulomb energy U in these Ni complexes is about 5 eV. The obtained results demonstrate that the 1-D Ni complexes are CT insulators.