Group mixed-valence copper

The copper atoms in the vast majority of the clusters can be assigned a formal charge of +1, while the chalcogen ligands are formally viewed as E or RE groups. Some of the selenium-bridged species, however - and nearly all copper telluride clusters - form nonstoichiometric compounds that display mixed valence metal centers in the formal oxidation states 0 and +I or +I and +11. These observations correlate with those made for the binary phases CU2S, Cu2 xSe, and Cu2- Te [38-40]. 

As mentioned before, a worthwhile model must possess a good accessibility of both the Cu(I) and Cu(II) oxidation states, and retain in solution not only the bimetallic unit but also any bridging group. To detect whether a proposed model of a Type III copper centre satisfies these requirements many studies on the cyclic voltammetry and/or the differential pulse polarography have been carried out and reported [157-210]. In some cases authors started with a di-copper(II) complex, in some other with a di-copper(I) complex and even eventually with a mixed-valence Cu(II)-Cu(I) dinuclear complex. 

IR results for a polymeric copper mixed-valence compound with a bridging 2-thioiso-orotato ligand show that the latter is coordinated through both carboxy-lato O atoms and the sulfur atom. The polymeric species [ Ag(pts) py]n, where pts = p-toluenesulfonate, shows IR bands due to both bidentate chelating and bridging sulfonato groups. ... 

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