Electronic structure of the quasi-one-dimensional halogen-bridged Ni complexes [Ni(chxn)2X]X2

Abstract

The electronic structure of the one-dimensional Ni complexes, ͓Ni͑chxn͒ 2 X]X 2 "XϭCl, Br; ͑chxn͒ϭ1R,2R-cyclohexanediamine…, is studied together with the discrete Ni complexes, ͓NiX 2 (͓14͔aneN 4 ͔͒ClO 4 "X ϭCl; Br;͓͑14͔aneN 4 ͒ϭ1,4,8,11-tetraazacyclotetradecane…,using optical spectroscopy, x-ray photoelectron spectroscopy ͑XPS͒ 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 ͑CT͒ energy ⌬ 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 compared with the Ni dihalides and the one-dimensional Pt complexes on the basis of the estimated parameter values of ⌬, T, and U.

Novel density-wave states of two-band Peierls-Hubbard chains

“…The phase boundary between M-SDW and X-SDW is roughly given by U X −U M = 1.8ε 0 . In comparison with MX compounds with M = Pt and M = Pd whose ground states are M-CDW, Ni complexes relatively have a small ε 0 and a large U M [26] and thus exhibit M-SDW ground states. In order to realize X-SDW ground states, a small enough ε 0 and a large enough U X are necessary.…”

Characterization of halogen-bridged binuclear metal complexes as hybridized two-band materials

“…However, the slightest interchain coupling stabilizes such fluctuations into a longrange order. The SDW states [17,28] widely observed in Ni complexes are thus stabilized, where hydrogen bonds and/or van der Waals contacts supply weak but essential interchain interactions. Therefore, concerning the SDW states as well, the present calculations remain suggestive.…”

Soliton Excitations in Halogen-Bridged Mixed-Valence Binuclear Metal Complexes

“…The PtX compounds [4][5][6] have mixed-valence ground states exhibiting intense and dichroic charge-transfer absorption, strong resonance enhancement of Raman spectra and luminescence with large Stokes shift. On the other hand, the NiX compounds [7][8][9] possess monovalence magnetic ground states due to the strong on-site d-d Coulomb interaction. Substituting the bridging halogens, ligand molecules and counter ions as well as the transition metals, we can widely tune the electronic states of MX chains [10].…”