Dimeric disulfido

The oxidation of [Cr(SH)(H20)5]2+ by I2 or Fe3+ under aerobic conditions in acid solutions gives the disulfido-bridged complexes [(H20)5CrS2Cr(H20)5]4+ and [(H20)sCr(S2H)Fe-(H20)5]4+ respectively (Scheme 100).967,968 The latter complex can also be obtained by substitution of chromium(III) in the former complex by iron(II) under acid conditions. The product distribution in the iron(UI) oxidation of [Cr(SH)(H20)5]2+ is pH dependent and at 298 K, pH = 1 the heteronuclear dimer [(H20)5Cr(S2H)Fe(H20)5]4+ constitutes over 80% of the product mixture. The rate of this reaction shows a [H+] 1 dependence, an observation consistent with [CrS(H20)5]+ being the kinetically active species. 

Characterization data (IR, molecular mass and S and Mo K-edge X-ray absorption spectroscopy) indicated that the Tp MoOS(OAr) compounds participate in a monomer(26)-dimer(29) equilibrium, favouring an oxosul-fido-Mo(vi) monomer in solution. " The compounds isolated depend on the steric bulk of the phenolate co-ligand. For example, the phenolate derivative crystallizes as dimeric [Tp MoOS(OPh)]2, which features Mo(v) centres linked by a bent p-disulfido bridge with Mo-S and S-S distances of 2.324(1) and 2.095(2) A, respectively. Figure 7.6(a) shows the closely related structure of [Tp "MoOS(OC6H3BuV3,5)]2 and the nature of the redox rearrangements involved in the monomer-dimer equilibrium. 

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