Mixed-valence complexes class

The frequency of infrared spectroscopy marks the frontier between average-valence complexes (class 3 below) and mixed valence complexes (class 2 below), and this technique is easily accessible. The unsymmetrical complexes belong to class 1 (below). 

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

Another type of complex for which it is obvious thatQlarge structural changes occur on excitation (probably 0.2-0.3 A) along particular coordinates are the infinite-chain mixed-valence complexes of platinum and palladium (class II, or localized mixed-valence complexes) (11).. These Pti [/PtIV, PdIVPtIV or Pdi [/PdIV... 

Mixed-valence complexes terminated in other than ammine and cyano ligands include [([9]aneS3)ClRu(/x-243)RuCl([9]aneS3)] which exhibits a strong intermetallic interaction consistent with a Robin-Day class III (delocalized) species. The synthesis of the Ru Ru complex [ P(OMe)3 2(MeCN)Ru(u-S2)(/u-NH2NH2)Ru P(OMe)3 2(MeCN)] + has been reported. Oxidation of the (M = Ru or Os) complexes [ 4 -(4-MeC6H4 tpy)M(u-L)M 4 -(4-... 

Complexes, see also specific type in solution, structures, see X-ray diffraction n-Complexes, 4 178-184 Complex formation constant, outersphere, 43 46, 55 electrovalent interaction in, 3 269-270 Compressibility coefficient of activation, 42 9 Comproportionation constants, class II mixed-valence complexes, 41 290-292 Comproportionation equilibrium, 41 280-281 Compton effect, 3 172 Conantokins, calcium binding, 46 470-471 Concanavalin A, 36 61, 46 308 Concensus motif, 47 451 Concentration-proportional titrations of poly-metalates, 19 250, 251, 254 Condensation... 

Electric fleld gradient, 22 214-218 Electroabsorption spectroscopy, 41 279 class II mixed-valence complexes, 41 289, 291, 294-297 [j(jl-pyz)]=+, 41 294, 296 Electrocatalytic reduction, nickel(n) macro-cyclic complexes, 44 119-121 Electrochemical interconversions, heteronuclear gold cluster compounds, 39 338-339 Electrochemical oxidation, of iron triazenide complexes, 30 21 Electrochemical properties fullerene adducts, 44 19-21, 33-34 nickeljll) macrocyclic complexes, 44 112-113... 

Humulene complexes with silver, 12 343, 346 Hund s rule, 13 162 HupU protein, 47 289 HupUV proteins, 47 190 Hush model, 41 274-280 class II mixed-valence complexes, parameters, 41 293... 

Molecular electronics, class II mixed-valence complexes, 41 303-304 Molecular light switch effect, 43 148 Molecular mechanisms, cobalt(III) hexaamines, 35 119-120 Molecular orbital calculations... 

These are one of the most studied classes of mixed valence complexes and have been reviewed recently by Keller and by Clark.134,135 They all possess a common structural unit X,MII X"M1V"X,MII, X. Table 5 gives a selection of examples for which electrical conduction studies are available with particular emphasis on results obtained on single crystals. The compounds are arranged depending on the charge of the complex. 

The immense amount of spectroscopic work carried out on these complexes, particularly on their electronic, infrared, Raman and resonance Raman spectra (2), has led to Wolffram s red being regarded as the archetypal class II or localized valence complex in which the two metal atoms differ in their oxidation states by two, cf. Prussian blue is so regarded for mixed-valence complexes in which the two metal atoms differ in their oxidation states by one. 

The intellectual push to study mixed-valence complexes was provided by the publication in 1967 of two review articles, by Allen and Hush (2) and Robin and Day (3), on the physical properties of mixed-valence systems. These were followed by Hush s publication (4) of his theoretical model of intervalence transitions, which provided a link between the properties of mixed-valence complexes in solution and the Marcus theory of intermolecular electron transfer (5, 6). The review by Robin and Day classified mixed-valence complexes into three types class I,... 

Fig. 3. Potential energy diagram for a symmetric class III mixed valence complex.

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