Superoxo complexes bridged

Nitrate dithionate dihydrate. The corresponding superoxo-bridged complex has similar structural data (109). Pentahydrate Co-N-Co angle is 97.2(1)J. 

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. ... 

A spectroscopic study of Claus blue, with comparisons to the much better characterized (180) ion [Rh2(0H)2(H20)n(/u,-02)]3+, was thus undertaken (181). By the use of UV-vis, ESR, and IR/Raman spectroscopies, as well as magnetic susceptibility measurements and voltamme-tric studies, it was determined that Claus blue solutions actually contain superoxo-dirhodium complexes, and not RhO2- ions. The su-peroxo bridge does not, however, derive from dioxygen, but from oxidation of coordinated hydroxide. Finally, Claus blue solutions were demonstrated to be good starting materials for the preparation of superoxo-dirhodium carboxylate complexes, which could be isolated and characterized. 

Redox equilibria between jU-peroxo-/i-hydroxo dicobalt(III) complexes and their oxidized superoxo-bridged form have been discussed in a recent review article by Fallab and Mitchell (119). Corresponding dirhodium(III) complexes have recently been reported (121-124). Reduction of peroxo- (or superoxo)-bridged dicobalt(III) complexes provides a method for inserting a hydroxo bridge, as shown in reaction Eq. (26) (323). 

This type of complex is derived from the mononuclear superoxo species via a further one-electron reduction of the dioxygen moiety. Cobalt is the only metal to form these complexes by reaction with dioxygen in the absence of a ligating porphyrin ring. Molybdenum and zirconium form peroxo-bridged complexes on reaction with hydrogen peroxide. In most cases the mononuclear dioxygen adducts of cobalt will react further to form the binuclear species unless specific steps are taken to prevent this. 

The superoxo bridged species of types (b) and (c) are again found mostly in Coni and Rhm species by oxidation of peroxo complexes, for example ... 

The majority of reported Co complexes in oxidation states higher than 3-1- contain noninnocent ligands, and this hence renders the assignment of metal oxidation state difficult. This problem has existed since Werner s time indeed, he initially formulated the superoxo-bridged dimers [(NH3)4Co(02)(NH2)Co(NH3)4] + and [(en)2Co(02)(NH2)Co(en)2]" + as mixed-valence peroxo-bridged Co(III)/(IV) complexes. One-electron oxidation of the unusual square-planar Co(III) complex (31) using Ce(IV) gives a deep blue low-spin species. This is soluble and stable in benzene, and exhibits a reversible one-electron reduction... 

The formation of the hydridohydroxo ion can be considered to be the result of stereoretentive oxidative addition of HjO across the (Rh(en)2]. Acidic solutions of [Rh(en)2(OH)(H)]+ are stable, even in the presence of O2, but in alkaline solution it reacts rapidly with oxygen, giving the hydroxoperoxo Rh " monomer, tra 5-[Rh(en)2(OH)(OOH)] (equation 165). Interference from the secondary reaction (equation 166) complicates the overall stoichiometry of the reaction. Concentration of this reaction mixture ([Rh(en)2(OH)2] -I- [Rh(en)2(OH)(OOH)]" ) in the presence of oxygen (pH 9-10) causes a color change to red and then to deep blue, with the formation of the superoxo-bridged Rh dimer, identified as [(H20)(en)2Rh02Rh(en)2(H20)] " . The transient red color is reminiscent of the electrochemical reduction of [Rh(NH3)4(OH)(OOH)] , which passes through a pink transient, after the consumption of 1F per Rh, tentatively identified as the hyd roxosuperoxo complex. ... 

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