SYNTHESIS, CHARACTERIZATION, AND STRUCTURE OF MIXED CHLORIDE-SELENIDETUNGSTEN CLUSTER COMPLEXES

The first examples of mixed halide-chalcogenide hexatungsten clusters as the molecular complexes, [W6Se8-xClx(PEt3)(6)](+), were prepared vi a the reaction of W6Cl12 With Na2Se and PEt3 in refluxing toluene. Sin gle crystals of the mixed chloride-selenide cluster cationic complexes were grown from chloroform solution. The structures of two crystals f rom different preparations, using Na2Se and K2Se as reagents, were det ermined and found to have different compositions, [W6Se7.0Cl1.0(PEt3)( 6)][Cl(CHCl3)(6)] and [W6Se6.4Cl1.6(PEt3)(6)][Cl(CHCl3)(6)], respectiv ely. In the latter case the crystal contains both the 20-electron clus ter [W6Se7Cl(PEt3)(6)](+) and the 21-electron cluster [W6Se6Cl2(PEt3)( 6)](+) in the mole fractions 0.40 and 0.60, respectively. The two crys tals were isomorphous: hexagonal, <R(3)over bar>, Z = 3, a = 18.921(4) Angstrom, c = 21.275(4) Angstrom and a = 18.908(5) Angstrom, c = 21.3 06(5) Angstrom, respectively. The bridging chlorine and selenium atoms are disordered over all the bridging ligand sites in both structures. In the unique [Cl(CHCl3)(6)](-) anion unit, six chloroform solvent mo lecules are octahedrally coordinated to a chloride anion via hydrogen bonding.