Nb x Ru6 - x Te8, New Chevrel-Type Clusters Containing Niobium and Ruthenium

Phases of composition Nb x Ru6 - x Te8 were prepared by reacting stoichiometric mixtures of the elements at high temperature in evacuated silica ampules. The structure of Nb3.33Ru2.67Te8 was refined from X-ray powder data using the Rietveld method. Nb3.33Ru2.67Te8 crystallizes isotypic with Mo6Q8 (Q = S, Se, Te) in the rhombohedral space group R3̄ with the hexagonal lattice parameters a = 10.34106(5) Å, c = 11.47953(7) Å, and Z = 3. Its structure consists of M6Te8 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 Ru6 - x Te8 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.