Syntheses, Structures and Solid-State Properties of MMX Mixed-Valence Chains, [NiII/III2(RCS2)4I]∞ (R = Et, n-Pr and n

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• 作者：Minoru Mitsumi ; Yuji Yoshida ; Akihisa Kohyama ; Yasutaka Kitagawa ; Yoshiki Ozawa ; Mototada Kobayashi ; Koshiro Toriumi ; Makoto Tadokoro ; Naoshi Ikeda ; Mitsutaka Okumura ; Mohamedally Kurmoo
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：July 20, 2009
• 年：2009
• 卷：48
• 期：14
• 页码：6680-6691
• 全文大小：1067K
• 年卷期：v.48,no.14(July 20, 2009)
• ISSN：1520-510X

文摘

The partial oxidation of [Ni^II/II₂(RCS₂)₄] (R = Et (1), n-Pr (2), and n-Bu (3)) with iodine affords the MMX chain compounds [Ni^II/III₂(RCS₂)₄I]_∞ (R = Et (4), n-Pr (5), and n-Bu (6)), respectively. The crystal structures of 4−6 consist of neutral one-dimensional (1-D) chains with a repeating −Ni−Ni−I− unit. The room-temperature (RT) structure of 4 indicates a charge-polarization (CP) state {—Ni^(2.5−δ)+−Ni^(2.5+δ)+-I⁻—Ni^(2.5−δ)+−Ni^(2.5+δ)+-I⁻— (δ 0.5)} close to an averaged valence state judged by the Ni−I distances. In contrast, 5 and 6 exhibit a 3-fold periodicity of a −Ni−Ni−I− unit due to the disorder of the dithiocarboxylato ligands. Compounds 4−6 show typical semiconducting behavior and exhibit an intense sharp absorption band centered at 5400 cm⁻¹, which is attributed to a Mott−Hubbard gap due to a relatively large on-site Coulomb repulsion energy U of the nickel atoms. The high-temperature magnetic susceptibilities of 4−6 can be described by a 1-D Heisenberg antiferromagnetic chain model with |J|/k_B ranging from 898(2) to 939(3) K. Compounds 4 and 5 undergo a spin-Peierls (SP) transition at relatively high T_sp = 47 and 36 K, respectively, which are accompanied by superlattice reflections corresponding to a 2-fold −Ni−Ni−I− period below T_sp. By determining the superstructure of 4 at 26 K, we conclude that the valence-ordered state changes from the CP in the RT phase to the alternate charge-polarization (ACP) state of —Ni^(2.5−δ)+−Ni^(2.5+δ)+-I⁻-Ni^(2.5+δ)+−Ni^(2.5−δ)+—I⁻— in the SP phase. Such a spin-Peierls transition could not be observed for 6.