Hiroshi OKAMOTO, Yuji SHIMADA, Yasuo OKA, Ashish CHAINANI, Takashi TAKAHASHI (Tohoku Univ.), Hiroshi KITAGAWA, Tadaoki MITANI (JAIST), Koshiro TORIUMI (Himeji Inst. Tech.), Kazuo IOUE, Toshio MANABE (Nagoya Univ.) and Masahiro YAMASHITA (Nagoya Univ. and IMS)
[Phys. Rev. B 54, 8438 (1997)]
The electronic structure of the one-dimensional Ni complexes, [Ni(chxn)2X]X2(X=Cl, Br, (chxn)=1R,2R-cyclohexanediamine), is studied by using optical spectroscopy, x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy. The optical spectra show that the Br compounds have a smaller 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 yields quantitative estimates for the charge transfer (CT) energy (DELTA) and the transfer energy T for discrete and one-dimensional Ni complexes. The analysis on the Ni LVV Auger spectra in conjunction with the valence 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, quite similar to the case of the Ni dihalides. The obtained results demonstrate that the one-dimensional Ni complexes are CT insulators. We discuss the differences in the electronic structures of the one-dimensional Ni complexes with the Ni dihalides and the one-dimensional Pt complexes on the basis of the estimated parameter values of (DELTA), T, and U.