On the Nature of Bridging Metal Atoms in Intermetalloid Clusters: Synthesis and Structure of the Metal-Atom-Bridged Zintl Clusters [Sn(Ge9 )2 ]4- and [Zn(Ge9 )2 )]6.

The addition of Sn and Zn ions to [Ge9 ] clusters by reaction of [Ge9 ]4- with SnPh2 Cl2 , ZnCp*2 (Cp*=pentamethylcyclopentadienyl), or Zn2 [HC(Ph2 P=NPh)2 ]2 is reported. The resulting Sn- and Zn-bridged clusters [(Ge9 )M(Ge9 )]q- (M=Sn, q=4; M=Zn, q=6) display various coordination modes. The M atoms that coordinate to the open square of a C4v -symmetric [Ge9 ] 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 Ge9 M fragments coordinate to a second [Ge9 ] cluster with similar orbitals but in different ways. The [Ge9 Sn]2- unit donates two electrons to the triangular face of a second [Ge9 ]2- cluster with D3h symmetry, whereas [Ge9 Zn]2- acts as an electron acceptor when interacting with the triangular face of a D3h -symmetric [Ge9 ]4- unit.