Mixed-valent complexes

A further dramatic comparison of the comparative reactivities of chromium alkyls in diverse oxidation states was furnished by another set of benzyl complexes. [7] Shown below, these three compound are isomers, yet they range in oxidation state from Cr to Cr °. Of the three, only the mixed-valent complex Cp G0i-ti n3-Bz)Cr(Bz)Cp, containing a Bivalent chromium bound to an T)3-benzyl and a ni-benzyl ligand, catalyzed the polymerization of ethylene. 

For the purposes of molecular electronics, the formation of solid-state multiple linear stacks, causing electron delocalization, favours electrical conductivity. Further, (partial) oxidation of such linear materials can produce non-stoichiometric (or mixed-valent) complexes like K175Pt(CN)4-1.5H20,9 and K1.62Pt(C204)2-2H20,8b which possess higher conductivity than their precursors. 

Our interest towards such derivatives is dictated by the fact that they are mixed-valent complexes, which means that electrons may easily flow along their metal frame. 

Figure5.20 Extended chain structure ofthe mixed-valent complex [Aul(CNcHex)2][Aulll(S2C6H4)2] showing the Au- -S contacts.

Cyanide complexes of platinum occur most commonly in the divalent state, although there has been increasing interest in the complexes formed with platinum in a higher oxidation state. Among the complexes most recently studied have been the mixed valent complexes where platinum cyanides in the divalent state are partially oxidized. These complexes form one-dimensional stacks with Pt-Pt interactions. In the solid state these materials show interesting electrical conductivity properties, and these compounds are discussed by Underhill in Chapter 60. In this section the preparative procedures and spectroscopy of the complexes will be covered, but for solid state properties the reader is referred to Chapter 60. 

The mixed-valent state was characterized by the near-infrared spectrum of the VOV+ complex, which was classified into a type II mixed-valent complex (a = 3.0 x 10 2) [111-114] the optical and electronic properties of VOV+ are based not only on the constituent components but also on their interaction [115]. 

It was recently shown [435] that the mixed-valent complex compounds with N-coordinated bridge fragment can be obtained on the basis of the nitride rhenium complex as a result of the transformation (3.202) ... 

CH2Ph)]. The former is an unusual 13-electron species whose coordinative unsaturation makes it an extremely effective catalyst for ethylene polymerization, and which exhibits a rich thermal decomposition chemistry. The latter, a mixed-valent complex exhibits ferromagnetic coupling between the two chromium atoms and is a catalyst for the polymerization of ethylene as well. ... 

Beyond the well known interest in the study of mixed-valent complexes [9], the incorporation of redox-actice ferrocene molecules into transition metal fragments is now opening promising fields of research. Heterometallic complexes able to undergo sequential electron-transfer steps have been shown to display the following ... 

The properties of the mixed valent complexes typified by I are unusual because of the nature of the low energy absorption, and unusual magnetic and electrical properties would be expected if the discrete dimer molecules interacted in the solid. Unusual optical, magnetic, and electrical properties are expected for mixed valent complexes of infinite length, i,e. going from Robin and Day Class III-A to Class III-B (21, 24),... 

Several 1-D inorganic complexes are comprised of alternating mixed valent complexes with long equivalent metal-metal spacings. Complexes of this type have been observed for Au -Au h Pd -Pd, and Pt -Pt (4, 6). The complexes of [M(amine)2X3] (X = halide) stoichiometry have halide atoms bridging the and atoms, but they are clearly associated with the tetravalent metal (6). The resultant properties are best described in terms of the sum of the individual molecules and are placed in Class II by Robin and Day (21, 24). Low conductivity has been observed for compounds of this type. 

Unconventional mixed-valent complexes of Ru and Os with heterocyclic ligands 07AG(E)1778. 

In recent years there has been increased interest in mixed valent homonu-clear complexes which exhibit unusual electronic properties arising from the rapid electron transfer between the metal sites, such that the metal atoms are in the equivalent nonintegral oxidation state. These complexes may have interesting electrical and magnetic properties via a valence interchange mechanism if interaction occurs between isolated clusters or within an infinite polymer. To date only small isolated oligomers have been characterized. General reviews of the mixed valent complexes are available for the interested reader (198, 355, 455, 468, 534). 

Several mixed valent complexes containing gold(lll) have been reported. Table XV. Several of these dichroic diamagnetic complexes exhibit a onedimensional structure in the solid with alternating square planar and linear M X " anions, (476, 480) (M = Au, X = Cl, I M = Ag, X = Cl) with a (Au - -X -X )j, linkage (476). A similar linkage is also... 

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