Halogen-bridged one-dimensional NiII-NiIV mixed-valence state and NiIII Mott-Hubbard state

M. Yamashita, E. Tsuruta, K. Inoue, T. Furuta, H. Okamoto, T. Mitani, K. Toriumi, H. Ohki, R. Ikeda

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Abstract

The halogen-bridged nickel compounds with linear-chain structure containing hetero-halogens as bridging and counter anions, Ni(chxn)2Cl2 459Br0, 541 (2) and Ni(chxn)2Cl1, 28Br1, 72 (3) (chxn=1R, 2R-diaminocyclohexane), have been synthesized by bromination of Ni(chxn)2Cl2 and chlorination of Ni(chxn)2Br2 in 2-methoxyethanol, respectively. Their structures have been determined by single-crystal X-ray diffraction method. In both (2) and (3), the Ni(chxn)2 moieties are bridged by halogens to construct linear-chain structures and hydrogen-bond networks of NH...X...HN which hold the chains are extended over the chains two-dimensionally. The bridging halogens in (2) and (3) are located at the midpoints between two nickel atoms on the chains, that is -NIII-X-NIII-structure with no Peierls distortion, indicating that these compounds take the Mott-Hubbard state as the same as the compounds containing homo-halogens, Ni(chxn)2Cl3 (1) and Ni(chxn)2Br3 (4) reported previously. The occupancy factors of Cl and Br in bridging and counter halogen sites in (2) and (3) are determined by X-ray analyses: [Ni(chxn)2ClxBr1-x]ClyBr2-y, x=0.976 and y=1.483 in (2) and x=0.68 and y=0.60 in (3). They show intense charge transfer bands in the visible region only with an electric vector parallel to the 1-D chain and their energies are in the order, (1)>(2)>(3)>(4). Substitution of the counter Cl- ions in [Ni(chxn)2Cl]Cl2 (1) with more bulky ClO4- ions succeeded in producing Ni(chxn)2Cl(ClO4)2 by a heterogeneous reaction. The solid state 13C NMR spectra suggest that Ni(chxn)2Cl(ClO4)2 take not the Mott-Hubbard state but the NiII-NiIV mixed-valence state formulated as [Ni(chxn)2][NiCl2(chxn)2](ClO4)4. These results indicate that the oxidation states of Ni atoms in these compounds are strongly affected by the kind of counterion through the hydrogen-bond and/or bulkiness.

Original languageEnglish
Pages (from-to)3461-3468
Number of pages8
JournalSynthetic Metals
Volume56
Issue number2-3
DOIs
Publication statusPublished - 1993 Apr 5

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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