METAL CLUSTERS SYNTHESIZED BY SOLID STATE REACTION——PREPARATION AND CRYSTAL STRUCTURE OF TWO MIXED METAL CLUSTERS,Ni_2Nb_2Te_4(Ⅰ) AND Ni_2Ta-2Te_4(Ⅱ)

摘要

The two title compounds obtained by solid state reaction at high temperature were char-acierized as isomorphism by single--crystal X--ray diffraction. The space group of both crys-tals is C2v4-Pma2, with lattice constants a = 7.955（1）, b=6.258 （1）, c=7 .203（2）A forI, and a =7.914 （1）, b=6.237 （1）, c=7.236 （1） ? for Ⅱ, Z=2. The structures were de-termined by normal method and refined to the final R = 0.074 and 0.083, respectively. Theresults show that the structure may be regarded as building by cluster unit with formulaNi2M2Te4 （M =Nb or Ta） in which two Ni atoms and two M atoms form a rhombus, whilethe Te atoms are distorted tetrahedrally coordinated with both kinds of metal atoms. In thecluster unit there exist interactions between Ni atoms as well as between Ni and M atoms.In addition, all the cluster units are linked together not only by bridging Te atoms, but alsoby weaker metal-metal interactions, so as to form two--dimensional network. Therefore, thestructure may be represented by the