Zintl ions, cage compounds, and intermetalloid clusters of Group 14 and Group 15 elements.

For a long time, Zintl ions of Group 14 and 15 elements were considered to be remarkable species domiciled in solid-state chemistry that have unexpected stoichiometries and fascinating structures, but were of limited relevance. The revival of Zintl ions was heralded by the observation that these species, preformed in solid-state Zintl phases, can be extracted from the lattice of the solids and dissolved in appropriate solvents, and thus become available as reactants and building blocks in solution chemistry. The recent upsurge of research activity in this fast-growing field has now provided a rich plethora of new compounds, for example by substitution of these Zintl ions with organic groups and organometallic fragments, by oxidative coupling reactions leading to dimers, oligomers, or polymers, or by the inclusion of metal atoms under formation of endohedral cluster species and intermetalloid compounds; some of these species have good prospects in applications in materials science. This Review presents the enormous progress that has been made in Zintl ion chemistry with an emphasis on syntheses, properties, structures, and theoretical treatments.

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.