Ge8R6: The ligands define the bonding situation within the cluster core

Abstract

The disproportionation reaction of Ge(I) halides open up a way to cluster compounds with an average oxidation state of the germanium atoms inside the cluster core in between 0 and 1. Simultaneously compounds with germanium in an oxidation state greater than I are formed. During the reaction of Ge(I) bromide with one equivalent of LiR (R = 2,6-(tBuO)₂C₆H₃) the cluster compound Ge₈R₆ and the molecular Ge(IV) compound R₃GeBr were isolated, representing the reduction and the oxidation product of the disproportionation reaction, respectively. The molecular structure of the Ge₈ cluster compound shows a highly different arrangement of the eight germanium atoms in the cluster core with respect to the only other Ge₈R₆ cluster compound where amido ligands are bound to the germanium atoms. Quantum-chemical calculations reveal that the distinct arrangement of the germanium atoms can be traced back to a different bonding situation inside the cluster frameworks, which is induced by the different ligands attached to the germanium atoms. These experimental and theoretical results show that the ligands are not only necessary for protecting the cluster core against the exterior but also have a strong influence on the bonding situation and therefore on the electronic situation inside the cluster core. Hence, the ligand influences the electronic properties and consequently the physical properties which is now seen, for the first time, in metalloid germanium cluster compounds.