Mixed valence complexes, halogen-bridge

Linear-chain Halogen-bridged Mixed Valence Complexes 149... 

Unusual behavior results from d7r-p7r interactions between open-shell metal ions and organic radicals as illustrated by the family of 3-D metals [Cu(R R -DCNQI)2] (DCNQI = 7V,A -dicyanoquinonediimine) (Figure 14). The halogen-bridged binuclear-metal mixed-valence complex, [Pt2(dta)4l] (dta = dithioacetate) (1-D linear chain Scheme 5a), exhibits metallic conduction above room temperature, representing the first example of a metallic halogen-bridged 1-D transition-metal complex. ... 

A. Quasi One-Dimensional Halogen-Bridged Mixed-Valence Complexes... 

A family of quasi one-dimensional halogen-bridged M /M mixed-valence complexes [M (en)2][M X2(en)2]Y4 (X = Cl, Br, I Y counterions such as CIO4) has been attracting interest among solid-state physicist and chemists. They display strong electron-lattice interactions and... 

Figure 14 Chemical structure of halogen-bridged mixed-valence complex [M(en)2][MX2(en)2) + (M = Pt, Pd, Ni X = Cl, Br, I) and electronic structures. Counter anions are omitted for clarity, (a) Spin density wave state (SDW) (b) charge density wave state (CDW).

Figure 18 schematically displays parts of CPK packing model for [Pt(en)2][PtCl2(en)2](20)4 in the yz plane (direction of coordination) and in the jny plane, respectively [95]. A minimum distance between aligned anionic head groups of double-chained amphiphiles is estimated as 5 A from CPK molecular model, and this value matches well with the Pt -Cl-Pt distance d) in the onedimensional complex. Therefore, it is reasonable that the halogen-bridged mixed-valence complex can be well preserved in polyion complexes. 

The localized-valence halogen-bridged platinum(II)/platinum(IV) complexes (175) are of interest because of their highly anisotropic electrical and optical properties. The complexes are characterized by broad and intense intervalence bands in their electronic spectra.542 Partial oxidation of [PtCl(dien)]Cl with iodine yields the mixed valence species [PtI(dien)][PtI3(dien)]I2,543 but when 4Me-dien is used, the mixed valence compound is only obtained if it is trapped quickly, before isomerization of the meridional platinum(IV) complex to a facial form.544 Although these species nominally have localized valences, the extent of delocalization increases as the bridging halide... 

The halogen-bridged mixed-valence transition metal complexes have a doubly degenerate linear chain structure,... 

These facts mean that the halogen-bridged mixed-valence transition metal complex qualifies a good one-dimensional compound with doubly degenerate structure (CDW). 

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