Dioxygen stretching frequencies

Vibrational Spectra. In his review Vaska discussed the dioxygen stretching frequencies measured in dioxygen complexes, and showed how the values then known fell into two groups. For and superoxo complexes the frequencies lay in the range... 

As originally pointed out by Vaska [26], dioxygen stretching frequencies of complexes known at that time could be divided into two... 

Dioxygen and its ions can bind in mononuclear and dinuclear structures in a number of ways,962 as illustrated in Scheme 1. The typical reaction of dioxygen with Co compounds involves a number of these binding forms, outlined in Scheme 2. Mononuclear Co111—peroxo complexes are relatively rare, but yellow trigonal bipyramidal complexes [Co(02)L2]+ (L = chelating phosphines dppe or dppp) have been characterized structurally where the 022 is bonded to the Co in the side-on r]2 form (Co—O 1.858(7) 1.881(4) A), with O—O stretching frequencies ( 870 cm-1) consistent with Coin-peroxo speciation.963... 

Busca (18b) has evaluated the literature values for infrared bands attributed to coordinated and adsorbed dioxygen species. He concludes that it is very difficult to deduce the nature of the dioxygen coordination from measurements of the frequency shift, Av00, with respect to the stretching frequency of the free molecule. It needs to be stressed that it is also difficult to distinguish between mononuclear and molecular species from measurements of v00, and this can only be achieved by careful interpretation of experiments using 160/180 isotopic mixtures. The absence of such experiments very often accounts for the conflicting attributions in the literature which are discussed in later sections. 

The complexes in Table I have been assigned an end-on geometry on the basis of spectroscopic data, chemical behavior, and, in the case of a macrocyclic rhodium complex, X-ray crystallographic data (53). The 0-0 stretching frequencies and 0-0 bond lengths are useful indicators of the electronic structure of coordinated dioxygen (54-59),... 

Type III. EPR-silent binuclear copper site that binds dioxygen as peroxide and exhibits unusual physicochemical characteristics (1) diamagnetism, (2) two characteristic absorption bands at 350 and 580 nm, and (3) a low O—O vibration stretching frequency (-750 cm-1). 

The stretching frequencies attributed to the 0-0 vibration are closely related to the structural type. Type I complexes show 0-0 stretching vibrations around 1125 cm-1 and type II around 860 cm-1. This sharp difference enables the O-O stretching frequency as measured by infrared or Raman spectroscopy to be used for structure type classification. Table 16.2.2 lists the structural data of dioxygen metal complexes. 

Table 52 Stretching Frequencies in Cobalt-Dioxygen Complexes...

Peroxo examples formed by the direct reaction with molecular dioxygen in the first row of the transition metals are few. One of the first examples of a peroxo vanadium complex formed by the direct reaction with dioxygen is a Tp Pr-bound seven-coordinate pentagonal-bipyramidal Vv complex Tp PrV0(f72-02)(pz PrH), with a relatively short O—O distance of 1.379(6) A and relatively high O—O stretching frequency of 960 cm-1, relative to typical peroxo species.14 First-row transition metalloproteins which bond molecular dioxygen are discussed, with their models, in Volume 8. 

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