Electronic stabilization effects: three new K-In-T (T = Mg, Au, Zn) network compounds

The ternary compounds K(34)In(91.05(9))Mg(13.95(9)) (I), K(34)In(96.19(6))Au(8.81(6)) (II), and K(34)In(89.95(1))Zn(13.05(7)) (III) have been synthesized by high-temperature means and structurally characterized by single-crystal X-ray diffraction methods. All are analogues of earlier products in which Li is substituted for some In in a hypothetical K(34)In(105) lattice. They consist of complex three-dimensional anionic networks built of In(12) icosahedra and M(28) triply fused icosahedra (M = In or In/T and T = Mg, Au, or Zn). The K atoms bridge between cluster faces or edges and form K(136) clathrate-IotaIota type networks. Two neighboring M(28) units are interconnected by an M atom to form a sandwich complex (M(28))M(M(28)) in I and II or by a Zn-Zn dimer in (M(28))ZnZn(M(28)) in III. Mixed In/T sites only occur in the M(28) portions. Phase stabilization through electronic tuning is present in all three via substitution of the electron-poorer T elements for In. Extended Hückel analyses indicate that all metal-metal bonding within the M(28) cluster appears to be optimized in I and III even though both are metallic. The size of the substituted element is also important in the structural features, as is especially shown by the Zn compound.