Synthesis and Characterization of Mo₆ Chalcobromides and Cyano-Substituted Compounds Built from a Novel [(Mo₆Brⁱ₆Yⁱ₂)L^a₆]<i>ⁿ</i>^- Discrete Cluster Unit (Yⁱ = S or Se and L^a = Br or CN)

The syntheses, crystal structures determined by single-crystal X-ray diffraction, and characterizations of new Mo6 cluster chalcobromides and cyano-substituted compounds with 24 valence electrons per Mo6 cluster (VEC = 24), are presented in this work. The structures of Cs4Mo6Br12S2 and Cs4Mo6Br12Se2 prepared by solid state routes are based on the novel [(Mo6Bri6Yi2)Bra6]4- (Y = S, Se) discrete units in which two chalcogen and six bromine ligands randomly occupy the inner positions, while the six apical ones are fully occupied by bromine atoms. The interaction of these two compounds with aqueous KCN solution results in apical ligand exchange giving the two first Mo6 cyano-chalcohalides: Cs0.4K0.6(Et4N)11[(Mo6Br6S2)(CN)6]3·16H2O and Cs0.4K0.6(Et4N)11[(Mo6Br6Se2)(CN)6]3·16H2O. Their crystal structures, built from the original [(Mo6Bri6Yi2)(CN)a6]4- discrete units, will be compared to those of the two solid state precursors and other previously reported Mo6 cluster compounds. Their redox properties and 77Se NMR characterizations will be presented. Crystal data: Cs4Mo6Br12S2, orthorhombic, Pbca (No. 61), a = 11.511(5) Å, b = 18.772(5) Å, c = 28.381 Å (5), Z = 8; Cs4Mo6Br12Se2, Pbca (No. 61), a = 11.6237(1) Å, b = 18.9447(1) Å, c = 28.4874(1) Å, Z = 8; Cs0.4K0.6(Et4N)11[(Mo6Br6S2)(CN)6]3·16H2O, Pm-3m (No. 221), a = 17.1969(4) Å, Z = 1; Cs0.4K0.6(Et4N)11[(Mo6Br6Se2)(CN)6]3·16H2O, Pm-3m (No. 221), a = 17.235(5) Å, Z = 1.