The formation of a metalloid Sn(10)[Si(SiMe(3))(3)](6) cluster compound and its relation to the alpha<-->beta tin phase transition.

Very recently it was shown that Sn monohalides can be prepared in preparative scale applying a preparative co-condensation technique. Here, a first reaction of Sn(i)Br is presented leading to the metalloid cluster compound Sn(10)[Si(SiMe(3))(3)](6) 1. This reaction can be seen as a first step to metalloid cluster compounds applying the disproportionation reaction of a metastable Sn monohalide. The ten tin atoms in 1 are arranged in the form of a centaur polyhedron, representing a novel structural motif in tin chemistry. The structural and electronic properties of 1 and its relation to the phase transition alpha<-->beta tin are discussed with the aid of quantum chemical calculations as well as (119)Sn Mössbauer spectroscopy.