Cobalt hydroxo-bridged complexes species

There are several examples of well-characterized tri- and tetranu-clear hydroxo-bridged complexes of chromium(III) and cobalt(III). Penta- and hexanuclear aqua chromium(III) complexes have been prepared in solution, but their structure and properties are unknown. Oligomers of nuclearity higher than four have not been reported for cobalt(IIl), with the exception of some hetero-bridged heteronuclear species (193, 194). There appear to be no reports of rhodium(III) or iridium(III) complexes of nuclearity higher than two. 

The complexes [LCo(p-02)(p-OH)CoL] [L = en, trien, dien, tetra-ethylenepentamine, or tris-(2-aminoethyl)amine] have been studied, and the new complexes [[Co(imidazole)(gly)2 202],4H20 [ Co2(imidazole)2-(gly)402 0H],3H20, and [Co(imidazole)(gly)2(02)H20] have been prepared The spectroscopic properties of various p-peroxo- and p-superoxo-cobalt(iii) complexes have been examined. The singly-bridged p-peroxo-compounds have a strong band at 300 nm, whereas this falls at 350 nm for p-peroxo-p-hydroxo-complexes and two peaks at 480 and 700 nm are observed for p-superoxo-species. The i.r. spectra of p-peroxo-bridged complexes of cobalt(iii)-cyclam have been reported. ... 

The data in Table XXXV show that common features for these ammonia and amine complexes are very fast isomerization between the cis and trans isomers of the diaqua species and the fact that the trans diaqua isomers are generally more stable than the cis isomers. In the ammine system the activation parameters for k2 and k 2 are consistent with an isomerization process at cobalt(III), but it is at present not clear how this occurs. It need not be a simple cis-trans isomerization occurring at one of the Co(III) centers, but might involve the participation of both metal centers. The isomerization reaction may proceed via intramolecular proton transfer between a water ligand and one of the two hydroxo bridges with simultaneous bridge cleavage and formation... 

The complex ions containing only hydroxo bridges (III and VI) are of interest because these are the only polynuclear cobalt (III) species which can be prepared directly from mononuclear cobalt (III) complexes. These ions are prepared by removing two moles of water from two moles of solid starting material—e.g., the sulfate of III is obtained by heating hydroxo-aquotetramminecobalt(III) sulfate (30) ... 

Oxidation of mandelic acid by H2O2, catalyzed by Fe ", is only 50% inhibited by the presence of OH radical traps and formation of an active Fe(IV) species may be a possibility. However it is thought more likely that the uninhibited pathway involves cage reaction of newly formed OH radicals. Peroxytungstic acids are formed in the H2O2 oxidation of dmso catalyzed by WO4 . An extensive study of the oxidation of cobalt(II) by m-Cl-perbenzoic acid in 90% acetic acid media has appeared. The mechanism is complex involving a second-order dependence on [Co(II)] and various dimeric and trimeric 0x0- and hydroxo-bridged species, are formed in the course of the reaction. 

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