High nuclearity clusters and beyond

Separate series of neutral and anionic osmium carbonyl clusters based on 3-20 osmium atoms have been prepared and characterised in the solid by single crystal X-ray analysis and in solution largely by13C NMR spectroscopy and vibrational analysis (IR). They appear to fall into two distinct series, viz., those which follow a polytetrahedral, non-metallic growth sequence, e.g. [Os3(CO)12] and [Os3(CO)11]2-, [Os4(CO)14] and [Os4(CO)13]2-, [Os5(CO)16] and [Os5(CO)15]2-, and [Os6(CO)18] and [Os6(CO)17]2-, and those which apparently follow the route to bcc packing, e.g. [Os6(CO)18]2-, [Os7(CO)21] and [Os7(CO)20]2-, [Os8(CO)23] and [Os8(CO)22]2-, [Os9(CO)24]2-, [Os10(CO)26]2-and [Os10C(CO)24]2-, and [Os20(CO)40]2-. Alternatively, the species [Os4(CO)14] and [Os4(CO)13]2-, [Os10(CO)26]2-and [Os10C(CO)24]2-and [Os20(CO)40]2-may be viewed as forming a 'magic number' sequence of clusters corresponding to the tetrahedral growth pattern, viz. 4, 10, and 20. Also described are the syntheses of mixed Os-C and Os-Hg clusters. The former bear a close resemblance to the carboranes in their structural features, whereas the Os-Hg clusters represent examples of linked cluster systems containing both transition metal and main group cluster domains. The geometric relevance that all these structures bear to the 'metallic state' is discussed.