Metalloid cluster compounds of germanium: novel structural motives on the way to elemental germanium!

Metalloid cluster compounds of germanium of the general formulae GenRm with n > m (R = ligand), where naked as well as ligand bound germanium atoms are present, represent a novel class of cluster compounds in group 14 chemistry, being ideal model compounds to get an insight into the area between the molecular and solid state. This borderland is of particular interest, especially for metals or semimetals, as drastic changes of physical properties take place during reduction from salt-like oxidized species (e.g. oxides, halides: non-conducting) to the bulk elemental phase (metal: conducting; semimetal: semiconducting). Therefore, interesting properties are expected for these intermediate compounds which might complement results from nanotechnology. During the last years a couple of different syntheses have been introduced, leading to metalloid clusters of germanium which exhibit new structures and bonding. In this review an account is given on the first steps in this novel field of group 14 chemistry. Special attention is focused on structural features and bonding properties.