On the Nature of Bridging Metal Atoms in Intermetalloid Clusters: Synthesis and Structure of the Metal-Atom-Bridged Zintl Clusters [Sn(Ge ) ] and [Zn(Ge ) )].

The addition of Sn and Zn ions to [Ge ] clusters by reaction of [Ge ] with SnPh Cl , ZnCp* (Cp*=pentamethylcyclopentadienyl), or Zn [HC(Ph P=NPh) ] is reported. The resulting Sn- and Zn-bridged clusters [(Ge )M(Ge )] (M=Sn, q=4; M=Zn, q=6) display various coordination modes. The M atoms that coordinate to the open square of a C -symmetric [Ge ] cluster form strong covalent multicenter M-Ge bonds, in contrast to the M atoms coordinating to triangular cluster faces. Molecular orbital analyses show that the M atoms of the Ge M fragments coordinate to a second [Ge ] cluster with similar orbitals but in different ways. The [Ge Sn] unit donates two electrons to the triangular face of a second [Ge ] cluster with D symmetry, whereas [Ge Zn] acts as an electron acceptor when interacting with the triangular face of a D -symmetric [Ge ] unit.