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New Routes to Transition Metal-Carbido Species:  Synthesis and Characterization of the Carbon-Centered Trigonal Prismatic Clusters [W6CCl18]n- (n = 1, 2, 3)

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posted on 27.08.2003, 00:00 authored by Eric J. Welch, Nathan R. M. Crawford, Robert G. Bergman, Jeffrey R. Long
Simultaneous reduction of WCl6 and CCl4 with bismuth metal at 400 °C affords a black solid, from which the new cluster [W6CCl18]2- is extracted into aqueous HCl. The cluster is isolated in 34% yield as (Bu4N)2[W6CCl18] and features a metal−metal bonded W6 trigonal prism centered by a carbon atom and surrounded by 12 edge-bridging and 6 terminal chloride ligands. A cyclic voltammogram of [W6CCl18]2- in DMF shows the cluster undergoes two reduction and two oxidation processes, suggesting five chemically accessible redox states. Consistent with this extensive electrochemistry, DFT calculations on the diamagnetic [W6CCl18]2- species reveal closely spaced frontier orbitals, with an a2‘ ‘ HOMO situated 0.61 and 0.71 eV below unoccupied e‘ ‘ and e‘ orbitals, respectively. Oxidation of the cluster by a single equivalent of NO+ gives [W6CCl18]-, which, as expected on the basis of the [W6CCl18]- HOMO character, possesses a less elongated W6 trigonal prism. Reduction of [W6CCl18]2- with a single equivalent of cobaltocene affords [W6CCl18]-, wherein population of a low-lying e‘ orbital leads to a significant Jahn−Teller distortion.