ELECTRONIC-STRUCTURE OF THE QUASI-ONE-DIMENSIONAL HALOGEN-BRIDGED NI COMPLEXES [NI(CHXN)(2)X]X(Z) (X=CL, BR) AND RELATED NI COMPOUNDS

The electronic structure of the one-dimensional Ni complexes, [Ni(chxn )(2)X]X(2)(X=Cl, Br; (chxn)=1R,2R-cyclohexanediamine), is studied toge ther with the discrete Ni complexes, [NiX(2)([14]aneN(4))]ClO4(X = Cl; ;([14]aneN(4))=1,4,8,11-tetraazacyclotetradecane), using optical spec troscopy, x-ray photoelectron spectroscopy (XPS) and Auger electron sp ectroscopy. The optical spectra show that the Br compounds have a smal ler gap as compared with the Cl compounds. An analysis using a simple X-Ni-X trimer model on the optical spectra and the Ni 2p XP spectra yi elds quantitative estimates for the charge transfer (CT) energy Delta and the transfer energy T for discrete and one-dimensional Ni complexe s. The analysis on the Ni LVV Auger spectra in conjunction with the va lence XP spectra indicates that the average on-side d-d Coulomb energy U in the one-dimensional and discrete Ni complexes is about 5 eV, qui te similar to the case of the Ni dihalides. The obtained results demon strate that the one-dimensional Ni complexes are CT insulators. We dis cuss the differences in the electronic structures of the one-dimension al Ni complexes compared with the Ni dihalides and the one-dimensional Pt complexes on the basis of the estimated parameter values of Delta, T, and Li.