Families of high nuclearity cages

The structural diversity displayed by polymetallic cages is discussed, concentrating on the chemistry of cobalt and nickel stabilised by carboxylate and pyridonate ligands. The structures can be broken down into "families of cages", five of which are identified. Adamantine-cages have been made with hepta- and nona-nuclear cores. Tricapped trigonal prisms with deca-, undeca- and dodeca-nuclear metal arrays have been made for Co and Ni, and related cages for Cr and Fe have also been synthesised. Perhaps the most aesthetically pleasing family are the metal wheels, which vary in nuclearity from eight to eighteen, and which have been found for the metals from Ti to Ni - excluding Mn. Cages based on oligomers of cubanes form the fourth family, and the fifth group is related to simple mineral archetypes such as the rock-salt or cadmium iodide structure.