Molecular growth from a Mo-176 to a Mo-248 cluster

In polyoxometalate chemistry a large variety of compounds, dusters and soli d-state structures can be formed by the linking together of well-defined me tal-oxygen building blocks(1,2). These species exhibit unusual topological and electronic properties and find applications ranging from medicine(3) to industrial processes(4). The recently reported ring-shaped mixed-valence p olyoxomolybdates of the type {Mo-154} (refs 5, 6) and {Mo-176} (refs 7, 8) represent a new class of giant clusters with nanometre-sized cavities and i nteresting properties for host-guest chemistry. Here we describe the format ion of related clusters of the type {Mo-248} formed by addition of further units to the inner surface of the {Mo-176} 'wheel'. The additional units ar range themselves into two {Mo-36} 'hub-caps' on the initial wheel-clusters that are not stable in isolation. These findings reveal a new pathway to th e development of complex coordination clusters.