Redox chemistry of the cluster [Os10C(CO)24]2-

Article abstract of DOI:10.1021/om00094a003

The dianion [Os₁₀C(CO)₂₄]^2- (1) is oxidized at a hanging drop mercury electrode (HDME) in a variety of media to produce [Os₂₀(C)₂(CO)₄₈Hg₂]^2- (2), which on standing ultimately yields the known [Os₂₀Hg(C)₂(CO)₄₈]^2- (3). The dianion 1 is readily reduced electrochemically (at wave A in the cyclic voltammogram) by two electrons to yield the tetraanion [Os₁₀C(CO)₂₄]^4- (5). This reduction was studied at a variety of electrodes and in different media and was found to be associated with an oxidation at more positive potentials (wave C). Electrochemical studies of 5 showed that 1 and 5 could be readily interconverted in close to 100% yield showing that the two redox processes were chemically reversible. From a comparison of the electrochemical and IR properties of 1 and 5 it was concluded that the two-electron reduction of 1 generated 5 with an associated minor change in structure, a process that was reversed upon oxidizing at wave C. When a solution of 1 is cooled, the two-electron wave (wave A) split into a quasi-reversible one-electron process and an irreversible wave which moved to more negative potentials as the temperature was reduced. The broad wave was linked to the oxidative feature (wave C) and demonstrated that the structural change occurs on the addition of the second electron to 1. The quasi-reversible electrochemical process was associated with the formation of the trianion [Os₁₀C(CO)₂₄]^3- (4) which could be independently synthesized by the slow chemical reduction of 1. As suggested by the electrochemical results, samples of 4 disproportionated at room temperature and hence could not be further characterized. The species 2-5 have been prepared by independent chemical methods.