Electronic structures of quasi-one-dimensional halogen-bridged Ni-III complexes with strong electron-correlations

In the quasi-one-dimensional halogen-bridged metal complexes, the Pt and Pd compounds have charge density wave (CDW) states or the M-II-M-IV mixed-val ence states where the bridging halogens are distorted from the midpoints be tween neighboring two metal ions due to the stronger electron-phonon intera ction. However, Ni compounds have spin density wave (SDW) states or the M-I II states where the bridging halogens are located at the midpoints between neighboring two metal ions, due to the stronger electron-correlation. These Ni compounds are not Mott-insulators but charge-transfer-insulators. The e lectronic structures in [Ni-III(chxn)(2)X]Y-2 (chxn = cyclohexanediamine; X = Cl, Br and mixed-halides; Y = Cl, Br, mixed-helides, NO3, ClO4 and BF4) are tuned by substituting the bridging halogens and counteranions. The comp etition between the SDW states in Ni-III sites and the CDW states in Pd-II- Pd-IV sites in the Ni-Pd mixed-metal compounds, Ni1-xPdx(chxn)(2)Br-3, has been investigated. The Pd-II-Pd-IV states are approaching the Pd-III states with increase of the Ni components in this system due to the stronger elec tron-correlation in Ni-III sites. (C) 1999 Elsevier Science S.A. All rights reserved.