Copper mixed valence complexes

Table 17 The Robin and Day Classification of Mixed Valence Complexes of the Copper(I) and (II) Ions340 362... 

It should be pointed out that most studies with cysteine have involved the naturally occurring l isomer. However, L-Pen is toxic so it is the enantiomeric D form that is therapeutically used. It is D-Pen that is used to remove the accumulated copper in sufferers of Wilson s disease consequently the interaction between copper and Pen has been intensively studied. At neutral pH a deep violet colour develops, the extent of formation of the colour being dependent on a number of factors solution pH, Cu" Pen ratio, 02 content, chloride ion concentration, A crystalline Tl1 salt isolated from neutral solution was shown to be a mixed valence complex of composition Tl Cug-Cu"(PenO)12Cl] (see Table 3). The same anion was shown to be the major species at neutral pH. A number of other mixed valence species involving Pen have since been isolated.24... 

The heteronuclear mixed-valence complexes 16b,c were obtained from H2L 15, triethylamine, and iron(III) chloride in the presence of an excess of cobalt(II) chloride or copper(II) chloride. In neutral 16b,c iron is present only in the oxidation state 3 , as unambiguously confirmed by Mossbauer spectroscopy, which reveals only one quadruple doublet. Cyclic voltammetric investigation of the redox-active metal centers of neutral 16b shows a reversible three-potential one-electron transfer process. The half-wave potentials of -660 and -1310 mV correspond to the redox processes [(Fe )2Co"OLf ] [Fe Fe Co OLf ]" [(Fe")2Co"OLf ] , whereas... 

A mixture of VOj and in HCIO4 gives a labile mixed-valence complex [ 203] with a formation constant of 8.1 M. The IT band is detected at 10,100cm". In methanol solution, a number of sulfur-bound copper(II) complexes, models for blue copper proteins, are reduced by ferrocene in a mechanism which involves formation of a precursor ion pair followed by rate-determining electron transfer. The activation parameters suggest that the precursor complex undergoes desolvation in the transition state. 

Victoriano et al. (1711,1712) reported that addition of thiuram disulfides to copper(I) halides gives mixed-valence complexes [Cu(S2CNR2)2][CuX (S2CNR2)] (R = Me, Et X = Cl, Br) containing one copper(III) and a second copper(II) center. Upon thermolysis (R = Me), electron transfer occurs generating the black copper(II) dimer [Cu(S2CNMe2)(p-Cl)]2 (Peff 1-81 BM) and one-half of an equivalent of tetramethylthiuram disulfide. 

In 1996 Stack and co-workers reported an unusual 3 1 (copper 02 stoichiometry) reaction between a mononuclear copper(I) complex of a A-permethylated (lR,2R)-cyclohexanediamine ligand with dioxygen. The end product of this reaction, stable at only low temperatures (X-ray structure at —40 °C) is a discrete, mixed-valence trinuclear copper cluster (1), with two Cu11 and a Cu111 center (Cu-Cu 2.641 and 2.704 A).27 Its spectroscopic and magnetic behavior were also investigated in detail. The relevance of this synthetic complex to the reduction of 02 at the trinuclear active sites of multicopper oxidases4-8 was discussed. Once formed, it exhibits moderate thermal stability, decomposed by a non-first-order process in about 3h at —10 °C. In the presence of trace water, the major isolated product was the bis(/i-hydroxo)dicopper(II) dimer (2). 

Rate and equilibrium constant data, including substituent and isotope effects, for the reaction of [Pt(bpy)2]2+ with hydroxide, are all consistent with, and interpreted in terms of, reversible addition of the hydroxide to the coordinated 2,2 -bipyridyl (397). Equilibrium constants for addition of hydroxide to a series of platinum(II)-diimine cations [Pt(diimine)2]2+, the diimines being 2,2 -bipyridyl, 2,2 -bipyrazine, 3,3 -bipyridazine, and 2,2 -bipyrimidine, suggest that hydroxide adds at the 6 position of the coordinated ligand (398). Support for this covalent hydration mechanism for hydroxide attack at coordinated diimines comes from crystal structure determinations of binuclear mixed valence copper(I)/copper(II) complexes of 2-hydroxylated 1,10-phenanthroline and 2,2 -bipyridyl (399). 

Figure 7.48 Two cytochrome c oxidase Cua center model compounds (A) delocalized core with two i-l,3-(KN KO)-ureate bridges as reported in reference 165-and (B) a dithiolate-bridged mixed-valence binuclear copper ion complex as re in reference 166.

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