Crystal Structures and Properties of MMX-Chain Compounds Based on Dithiocarboxylato-Bridged Dinuclear Complexes
In this chapter, a comprehensive study of the syntheses, crystal structures, and properties of the series of one-dimensional (1D) halogen-bridged mixed-valence dimetal complexes, MMX-chain compounds, based on the dithiocarboxylato-bridged dinuclear comple
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Crystal Structures and Properties of MMX-Chain Compounds Based on Dithiocarboxylato-Bridged Dinuclear Complexes Minoru Mitsumi
Abstract In this chapter, a comprehensive study of the syntheses, crystal structures, and properties of the series of one-dimensional (1D) halogen-bridged mixed-valence dimetal complexes, MMX-chain compounds, based on the dithiocarboxylato-bridged dinuclear complexes, [Pt2(RCS2)4I]1 (R ¼ Me (1), Et (2), n-Pr (3), n-Bu (4), n-Pen (5), and n-Hex(6)) and [Ni2(RCS2)4I]1 (R ¼ Me (7), Et (8), n-Pr (9), and n-Bu (10)) are described. The evolution from 1D halogenbridged metal complex, MX-chain compounds, to MMX-chain compounds has produced a variety of electronic states and subtle balance of solid-state properties originating from the charge–spin–lattice coupling and the fluctuation of these degrees of freedom. With increasing the internal degrees of freedom originating from the mixed-valence diplatinum unit, the Pt MMX-chain compounds except for 3 show relatively high electrical conductivity of 0.84–43 S cm–1 at room temperature and exhibit metallic conducting behavior with TM–S ¼ 205–324 K. These compounds at room temperature are considered to take the valence-ordered state close to an averaged-valence (AV) state of –Pt2.5+–Pt2.5+–I––. The analyses of the diffuse scattering observed in the metallic state of 2 revealed that the metallic state has appeared by the valence fluctuation accompanying the dynamic valence-ordering state of the charge-density-wave (CDW) type of –Pt2+–Pt2+–I––Pt3+–Pt3+–I––. On the other hand, the metallic Pt MMX-chain compounds become insulators with lowering temperature due to the lattice dimerization originating from an effective half-filled metallic band. The synchrotron radiation crystal structure analysis of 2 at 48 K revealed that the valence-ordered state in the LT phase is the alternate chargepolarization (ACP) state of –Pt2+–Pt3+–I––Pt3+–Pt2+–I––. Furthermore, the elongation of the alkyl chains introduces increasing motional degrees of freedom in the
M. Mitsumi (*) Department of Material Science, Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan e-mail: [email protected] M. Yamashita and H. Okamoto (eds.), Material Designs and New Physical Properties in MX- and MMX-Chain Compounds, DOI 10.1007/978-3-7091-1317-2_9, # Springer-Verlag Wien 2013
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system. Interplay between electronic degrees of freedom and molecular dynamics is also expected to cause an intriguing structural phase transition accompanying an electronic and/or magnetic transition never observed for [M2(MeCS2)4I]1 (M ¼ Pt (1), Ni (7)). With the elongation of alkyl chains in dithiocarboxylato ligands, the compounds 3–5 undergo two phase transitions at near 210 K and above room temperature, indicating the existence of the LT, RT, and HT phases. The periodicity of crystal lattice in the RT phase of 3–5 along 1D chain is threefold of a –Pt–Pt–I– unit, and the structural disorders have occurred for the dithiocarbo
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