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 SnPh₂Cl₂, ZnCp*₂(Cp*=pentamethylcyclopentadienyl), or Zn₂[HC(Ph₂P=NPh)₂]₂is 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 C_4v-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 Ge₉M fragments coordinate to a second [Ge₉] cluster with similar orbitals but in different ways. The [Ge₉Sn]²⁻unit donates two electrons to the triangular face of a second [Ge₉]²⁻cluster with D_3hsymmetry, whereas [Ge₉Zn]²⁻acts as an electron acceptor when interacting with the triangular face of a D_3h-symmetric [Ge₉]⁴⁻unit.