MIXED CO-NI CARBIDE CLUSTERS .1. SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF THE [Co3NI9C(CO)20]3- TRIANION

Reaction of [Co3(CO)9CCl] with [Ni6(CO)12]2- results in a complicated mixture of mixed Co-Ni carbide carbonyl clusters, among which the [Co3Ni9C(CO)21]3- trianion has been isolated in a pure crystalline state and fully characterized by X-ray crystallography. The metal framework of this compound is unprecedented in cluster geometries and may be described as a square antiprism of metal atoms tetra-capped on two alternate pairs of adjacent triangular faces. Despite the presence of a caged carbon atom in the square-antiprismatic cavity, the compound is readily degraded by carbon monoxide (25 "C, 1 atm) mainly to a mixture of [Co(CO)4]- and [Ni(CO)4]. Corresponding degradation of the cluster under a mixture of carbon monoxide and hydrogen yields, in addition, trace amounts of organics, mainly C1 and C2 hydrocarbons, probably derived from the carbide atom.