Nb(x)()Ru(6)(-)(x)()Te(8), New Chevrel-Type Clusters Containing Niobium and Ruthenium(,)

Phases of composition Nb(x)()Ru(6)(-)(x)()Te(8) were prepared by reacting stoichiometric mixtures of the elements at high temperature in evacuated silica ampules. The structure of Nb(3.33)Ru(2.67)Te(8) was refined from X-ray powder data using the Rietveld method. Nb(3.33)Ru(2.67)Te(8) crystallizes isotypic with Mo(6)Q(8) (Q = S, Se, Te) in the rhombohedral space group R&thremacr; with the hexagonal lattice parameters a = 10.34106(5) ?, c = 11.47953(7) ?, and Z = 3. Its structure consists of M(6)Te(8) mixed-metal clusters (M = Nb, Ru) which are connected by intercluster M-Te bonds to form a three-dimensional network. Metal-metal bonding in these phases is analyzed in terms of Pauling bond orders and found to be weaker compared to that in related cluster compounds. Nb(x)()Ru(6)(-)(x)()Te(8) are the first representatives of Chevrel-type cluster phases with complete substitution of Mo by other metals. The chemical perspectives arising from this substitution are discussed.