From platinum blues to rhodium and iridium blues

Platinum blues constitute an intriguing and extensively studied family of c omplexes generally containing a chain of four platinum atoms of mixed valen ces and metal-metal bonds. There is no reason why they should constitute an isolated type of complexes based exclusively on platinum, and we comment o n a rational strategy for the preparation of a new family of rhodium and ir idium blues. The most effective approach seems to be a redox condensation b etween dinuclear complexes of a given metal in different oxidation states t o yield the desired tetrametallic chain. Thus, by mixing equimolar amounts of dinuclear rhodium or iridium pyrazolato (pz) complexes in oxidation stat es I and II, [{M(mu-pz)(CNtBu)(2)}(2)] and d[{Mu-pz)(CNtBu(2))(NCME}(2)](PF 6)(2), novel Phodium and iridium pyrazolato blues of formula [{M(mu-pz)(CtN rBu)(2)}(4)] (PF6)(2) are obtained by a redox condensation. Alternatively, the oxidation of just one half of the dinuclear rhodium(I) or iridium(I) co mplexes can be carried out with a conventional oxidant, such as [FeCp2]PF6, in such a way that after the redox condensation the four metal atoms end u p with a formal oxidation state of 1.5. In same cases, a direct partial oxi dation of diiridium(I) complexes with diiodine can also be effective. Final ly, a few comments of concern for the possible development of related linea r polynuclear mixed-valence complexes are presented.