Polyhedral nine-atom clusters of tetrel elements and intermetalloid derivatives.

Homoatomic polyanions have the basic capability for a bottom-up synthesis of nanostructured materials. Therefore, the chemistry and the structures of polyhedral nine-atom clusters of tetrel elements [E(9)](4-) is highlighted. The nine-atom Zintl ions are available in good quantities for E = Si-Pb as binary alkali metal (A) phases of the composition A(4)E(9) or A(12)E(17). Dissolution or extraction of the neat solids with aprotic solvents and crystallization with alkali metal-sequestering molecules or crown ethers leads to a large variety of structures containing homoatomic clusters with up to 45 E atoms. Cluster growth occurs via oxidative coupling reactions. The clusters can further act as a donor ligand in transition metal complexes, which is a first step to the formation of bimetallic clusters. The structures and some nuclear magnetic resonance spectroscopic properties of these so-called intermetalloid clusters are reviewed, with special emphasis on tetrel clusters that are endohedrally filled with transition metal atoms.