Halides of the Heavier Group 14 Homologues Germanium, Tin, and Lead-A Journey through Unusual Compounds and Oxidation States.

Classical halides of the heavier Group 14 homologues germanium, tin, and lead are common precursors for the synthesis of exciting compounds, such as polyhedral clusters. To get access to larger metalloid cluster compounds of Group 14, the disproportionation reaction of metastable monohalide solutions, accessible through a preparative co-condensation reaction, proved to be quite successful. As the identity of the subvalent halides within the metastable solutions were yet unknown the reaction course from a monohalide precursor to a metalloid cluster was mostly unidentified. This might change now, as a first subhalide cluster [Ge14 Br8 (Et3 P)4 ] could be characterized, being the first trapped intermediate of the disproportionation reaction of Group 14 subhalides. All these aspects are included within this Minireview, together with a short historical overview, dealing with the development of the preparative co-condensation technique out of the matrix isolation technique, being the essential first step of the synthesis of metastable monohalide solutions of the heavier Group 14 elements Ge and Sn.