Control of charge instabilities in quasi-one-dimensional halogen-bridged nickel compounds

Quasi-one-dimensional halogen-bridged nickel compounds with nitrate counteranions, Ni(chxn)zX(N03)E (chxn=cyclohexanediamine; X=C1 and Br), and with Perchlorate counteranions, Nl(chxn)2X(C10A)e (X=C1 and Br) have been synthesized in order to control the charge instabilities. The Ni(chxn)eX(N03)2 were synthesized by both chemical and electrochemical methods. The crystal structure of Ni(chxn)2Br(NO3)2 has been determined by single-crystal X-ray diffraction method. In this compound, the Ni(chxn)E moieties are bridged by Br- ions to construct linear-chain structures and the hydrogen-bond networks of NH…O-N-O…HN which hold the chains are extended over the chains two-dimensionally. The bridging Br˜ ions are located at the midpoints between neighboring two Ni atoms along the chains with no Peierls distortion. The Ni(chxn)EX(C104)2 were synthesized by halogenation of 70 % HC10 solution of Ni(chxn)2(C10J2. The lattice constants of Ni(chxn)2Cl(C104)E were determined by X-ray powder pattern. The N1-C1-N1 distance of this compound is almost equal to that of Ni(chxn)2Cl3. but the interchain distance in the direction of counteranions is much longer than that in Ni(chxn)2Cl3. The electronic structure of Ni(chxn)2Cl(C104)2 was discussed on the basis of the results of electrical conductivity and temperature-dependence CP/MAS 13C NMR spectra.