Superoxide stretching frequencies

The superoxide complexes typically bind end-on r/1 though this is not always the case, as in TpCon02 (Tp = hydridotris(3-tert-butyl-5-methylpyrazolyl)borate) (3),12 in which the superoxo species was found to bind rj1. Interestingly this compound had an O—O stretching frequency between superoxo and peroxo species of 961 cm-1, though the crystal structure showed the O—O bond to be 1.262 A, identifying it as a superoxo species. 

This classification is only a formalism, remembering that electron transfer from the metal complex to the bound O2 moiety is not complete. Thus superoxide-like does not mean superoxide ion, but the O—O stretching frequencies (I o—o. Table 1) and the... 

Scatter diagram showing the distribution of O — O stretching frequencies and separations in ionic superoxides and peroxides (A) and in coordination compounds. An open circle denotes O2 coordinated to one metal a filled circle denotes O2 bridging two metals. The O — O stretching frequencies of oxyhemoglobin, oxyhemocyanin, and oxyhemerythrin are marked by dashed lines. 

The emerging EPR active superoxide anion species O2 is complexed by a cation (which must not necessarily be a constituent of the anion vacancy) and interacts now with the IR active OH group previously involved in the H bond with the colour centre electron [22,25], The gzz signal component of O2 is sensitively influenced by the local crystal field of the complexing cation [31,32], On the other hand the OH stretching frequency depends on the strength of the interaction of OH with O2, Thus the redox reaction described by eq,6 may be monitored by EPR and IR spectroscopy. In Fig,5 the respective curves are compared for fundamentally different experimental conditions ... 

The 0-0 stretching frequency of 1107 cm for oxyhemoglobin was often cited " as evidence that the superoxide anion 0 is bonded to low-spin... 

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