Metal carbonyl cluster
In chemistry, a metal carbonyl cluster is a compound that contains two or more metals linked in part by metal-metal bonds and containing carbon monoxide (CO) as the exclusive or predominant ligand. Simple examples include Fe2(CO)9, Fe3(CO)12, Mn2(CO)10. High nuclearity clusters include [Rh13(CO)24H3]2− and the stacked Pt3 triangules [Pt3n(CO)6n]2− (n = 2–6).
Binary carbonyl clusters consist only of metal and CO. They are the most widely studied and used metal carbonyl clusters. They arise in general by the condensation of unsaturated metal carbonyls. Dissociation of CO from Ru(CO)5 would give Ru(CO)4, which could trimerize to Ru3(CO)12. The reaction mechanisms are more complicated than this simple scenario. Condensation of low molecular weight metal carbonyls requires decarbonylation, which can be induced thermally, photochemically, or using various reagents. The nuclearity (number of metal centers) of binary metal carbonyl clusters is usually no greater than six.
Chini clusters follow the general formula of [Pt3(CO)6]n2−,1 < n < 10. These clusters are prepared by reduction of hexachloroplatinate with strongly basic methanol under an atmosphere of CO. These clusters consist of stacks of triangularly shaped Pt3 subunits. Although these clusters were first reported in 1969 by Chatt and Booth, their structure were not established until Chini and Longoni’s work in 1976.
Chini clusters are based on a planar triangular building block that can be condensed as multiple units forming chains usually anywhere from two to ten units long. The chains are formed by stacking of the planar units, extending through platinum to platinum bonds forming trigonal prismatic clusters. Within a triangular unit, the platinum-platinum bond lengths are 2.65 Å and between units the Pt---Pt bond lengths are 3.05 Å. Cluster structure is easily disrupted by deposition onto surfaces such as carbon or silicon, where the chains are broken, but the triangular subunits remain intact. The tetramer [Pt3(CO)6]42− is the most common member of this series of clusters. These clusters undergo reversible redox. They catalyze the hydrogenation of alkenes, ketones, aldehydes.
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