Molecular growth from a Mo176 to a Mo248 cluster

In polyoxometalate chemistry a large variety of compounds, clusters and solid-state structures can be formed by the linking together of well-defined metal–oxygen building blocks1, 2. These species exhibit unusual topological and electronic properties, andfind applications ranging from medicine3 to industrial processes4. The recently reported ring-shaped mixed-valence polyoxomolybdates of the type {Mo154} (refs 5, 6) and {Mo176} (refs 7, 8) represent a new class of giant clusters with nanometre-sized cavities and interesting properties for host–guest chemistry. Here we describe the formation of related clusters of the type {Mo248} formed by addition of further units to the inner surface of the {Mo176} ‘wheel’. The additional units arrange themselves into two {Mo36} ‘hub-caps’ on the initial wheel—clusters that are not stable in isolation. These findings reveal a new pathway to the development of complex coordination clusters.