Synthesis and characterization of reduced tungsten sulfide cluster complexes

Abstract

<p>Reduction of tungsten(IV) chloride with metals was studied in order to find a high-yield and convenient preparation of [alpha]-tungsten(II) chloride. The reduction of tungsten(IV) chloride with iron metal proved to be the most convenient and reliable synthesis, with a good yield of 60%;Complete substitution of sulfide for chloride in W[subscript]6Cl[subscript]8[superscript]4+ was achieved in the presence of sodium n-butoxide in pyridine solution. The resulting W[subscript]6S[subscript]8 cluster was stabilized by coordination of pyridine (py) ligands. The initial product W[subscript]6S[subscript]8(py)[subscript]6 is a poorly crystalline powder which is not soluble in organic solvents including pyridine;The triethylphosphine (PEt[subscript]3) and tetrahydrothiophene (THT) complexes of W[subscript]6S[subscript]8 were established by ligand displacement of pyridine in W[subscript]6S[subscript]8(py)[subscript]6. Structures for both W[subscript]6S[subscript]8(PEt[subscript]3)[subscript]6·1.44CH[subscript]2Cl[subscript]2 and W[subscript]6S[subscript]8(THT)[subscript]6 were determined by single crystal x-ray diffraction. Triethylphosphine coordinated to the W[subscript]6S[subscript]8 cluster unit most strongly, while the pyridine ligand was most labile among these organic ligands;Each adduct of W[subscript]6S[subscript]8 showed bands characteristic of the coordinated ligand, and all of them showed bands attributed to the internal modes of the W[subscript]6S[subscript]8 cluster unit. This cluster unit has 20 electrons for metal-metal bonding, compared to 24 electrons for W[subscript]6Cl[subscript]8[superscript]4+. The change of W-W distance, derived from results of the structure determinations clearly reflects removal of electrons from M-M bonding orbitals on passing from the 24 to the 20 electron clusters. The nearly perfect octahedral symmetry of the cluster units, and their diamagnetic susceptibility, confirms that there is no orbital degeneracy in the ground state of these complexes;These adducts are the first examples of model molecular complexes of the W[subscript]6S[subscript]8 cluster unit, which is not known in solid state phases analogous to the well-known Chevrel phases, M[subscript]xMo[subscript]6S[subscript]8. The latter compounds have been extensively investigated, and are known to possess rich and exciting physical and chemical properties. Attempts were made in this work to remove coordinated ligands from the W[subscript]6S[subscript]8 cluster unit, towards the goal of establishing the still unknown "tungsten Chevrel phases". From the preliminary studies it was found that the pyridine complex of W[subscript]6S[subscript]8 could not be completely deligated without disruption of the W[subscript]6S[subscript]8 cluster, either in solid state reactions or reactions performed in solutions. (Abstract shortened with permission of author.)</p>