Sc5Ni2Te2:: Synthesis, structure, and bonding of a metal-metal-bonded chain phase, a relative of Gd3MnI3

Sc5Ni2Te2 has been prepared by high-temperature solid-state techniques and the structure determined at 23 degrees C by single crystal and powder X-ray diffraction methods to be orthorhombic, Pnma (No. 62) with Z = 4, a = 17.862(1) Angstrom, b = 3.9533(3) Angstrom, c = 10.6398(6) Angstrom. The structure contains pairs of eclipsed zigzag chains of nickel atoms that are sheathed by scandium atoms and demarcated from other chains by tellurium atoms. The structure is isotypic with that of Hf5CO1+xP3-x, but Shifted atomic positions and a different ordering of the main group and late transition elements give it a clearly 1D character. The differences in dimensionality, ordering, and bonding are discussed, and comparisons are made with Gd3MnI3 and rare-earth-metal cluster halides in general.