NBXRU6-XTE8, NEW CHEVREL-TYPE CLUSTERS CONTAINING NIOBIUM AND RUTHENIUM

Phases of composition NbxRu6-xTe8 were prepared by reacting stoichiome tric mixtures of the elements at high temperature in evacuated silica ampules. The structure of Nb3.33Ru2.67Te8 was refined from X-ray powde r data using the Rietveld method Nb3.33Ru2.67Te8 crystallizes isotypic with Mo(6)Q(8) (Q = S, Se, Te) in the rhombohedral space group <R(3)o ver bar> with the hexagonal lattice parameters a = 10.34106(5) Angstro m, c = 11.47953(7) Angstrom, and Z = 3. Its structure consists of M(6) Te(8) mixed-metal clusters (M = Nb, Ru) which are connected by intercl uster M-Te bonds to form a three-dimensional network. Metal-metal bond ing in these phases is analyzed in terms of Pauling bond orders and fo und to be weaker compared to that in related cluster compounds. NbxRu6 -xTe8 are the first representatives of Chevrel-type cluster phases wit h complete substitution of Mo by other metals. The chemical perspectiv es arising from this substitution are discussed.