Edge-bridged octahedral tungsten-oxygen-chlorine clusters: Synthesis and characterization of two D-3d-symmetric [W6O6Cl12](2-) isomers and [W6O7Cl11](3-)

Initial access to the chemistry of hexanuclear tungsten oxohalide clusters is provided through the reduction of WOCl4 with bismuth metal at 360 degree sC. Reactions targeting W6O6Cl10 produce an amorphous black solid, which, u pon treatment with concentrated aqueous HCl, releases the edge-bridged octa hedral cluster [alpha -W6O6Cl12](2-) into solution. The cluster exhibit, a D-3d-symmetry structure in which the six oxygen atoms bridge the edges betw een two opposing triangular faces of a trigonally compressed W-6 octahedron . Reactions incorporating additional bismuth metal yield a mixture of solub le clusters, including a 5:7 ratio of [alpha -W6O6Cl12](2-) and another D-3 d-symmetry isomer, [beta -W6O6Cl12](2-). The latter species displays a diff erent core structure, in which the six oxygen atoms are situated on the edg es comprising two opposing triangular faces of a trigonally elongated W-6 o ctahedron. Isolated as the BuN+ salts, the two isomers can be separated by a process relying on the differences in crystal morphology. Cyclic voltamme try of acetonitrile solutions shows two reversible one-electron reductions for each cluster, the a isomer being slightly more easily reduced. Density functional theory calculations indicate that the two isomers of [W6O6Cl12]( 2-) are nearly identical in energy, with the beta isomer lying just 1.4 kca l/mol below the a. isomer. The other major product isolated from the reacti on with additional bismuth is [W6O7Cl11](3-), a cluster at least formally r elated to [beta -W6O6Cl12](2-) by Substitution of an O2- ion for a core Cl- ion. In acetonitrile solution, this cluster displays a single reversible o ne-electron reduction. It is anticipated that the reactions elaborated hen will lead to a general method for synthesizing metastable metal oxohalide c lusters.