The synthesis and reactivity of the heptanuclear dianion [Os₇(CO)₂₀]^2- including the synthesis and structural characterizations of the compounds [Os₇(CO)₂₀(AuPEt)₃₂] and [Os₈(CO)₂₀(η⁶-C₆H₆]

Reduction of the heptaosmium cluster [Os₇(CO)₂₁] With [Et₄N][NH₄) gives the cluster dianion [Os₇(CO)₂₀]^2-, 1, in high yield. The reaction of the dianion with [AuP R₃Cl] (R=Et or Ph) in the presence of TlPF₆ forms [Os₇((CO)₂₀(AuP R₃)₂] [R=Et (2a);R = Ph(2b)] in 80% yield, while the corresponding reaction with (Os(C₆H₆)(CH₃CN)₃]²⁺ gives [Os₈(CO)₂₀ (η⁶-C₆H₆)] (3) in reasonable yield (ca. 30%). The dianion, 1, and the clusters 2 and 3 have been fully characterized by bout spectroscopic and crystallographic methods. The crystal structure of the [Ph₄P]⁺ salt of 1 shows that the metals in the anion adopt a capped octahedral geometry, with all twenty carbonyl ligands in terminal sites. The metal core geometry in 2a is best described as a tricapped octahedron, and is based on the structure of the dianion 1 with two adjacent octahedral faces capped by the Au atoms of the two AuPEt₃ groups. In a similar fashion, the geometry of 3 is related to that of 1 with the addition of an Os(C₆H₆) unit capped to a triangular face, to give a bicapped octahedral framework.