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

Abstract

Simultaneous reduction of WCl6 and CCl4 with bismuth metal at 400 degrees 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]1-, which, as expected on the basis of the [W6CCl18]2- HOMO character, possesses a less elongated W6 trigonal prism. Reduction of [W6CCl18]2- with a single equivalent of cobaltocene affords [W6CCl18]3-, wherein population of a low-lying e' orbital leads to a significant Jahn-Teller distortion.

Nitric Oxide Activation by Distal Redox Modulation in Tetranuclear Iron Nitrosyl Complexes

“…20-21 Hexanuclear complexes with multiple reversible metal-based redox-events (≥ 3) have been reported as well. 22 For example, a hexanuclear iron cluster has been shown to support up to five redox events spanning a potential window of only 1.3 V. 22b Recently reported bimetallic complexes of first-row transition metals exhibited multiple redox-events as well, in contrast to their monometallic counterparts. 23 Other notable examples include mononuclear complexes of the type [M(bpy) 3 ] n (n = 3 + , 2 + , 1 + , 1 − , 2 − , and 3 − ), although in these cases many of the redox-events are ligand based.…”

Using EPR to follow reversible dihydrogen addition to paramagnetic clusters of high hydride count: [Rh6(PCy3)6H12]+and [Rh6(PCy3)6H14]+

“…7, 11 There is a more general interest in the redox chemistry and magnetism of transition metal clusters, and a number of examples have been reported of cluster species that support sequential redox events and/or show paramagnetism in isolated species. [12][13][14][15][16][17] For example [W 6 CCl 18 ] n-(n = 0 to 4), 18 [W 6 NCl 18 ] n-(n = 1 to 3), 19 [FeS 8 (PEt 3 ) 6 ] n+ (n = 0 to 4) 20 and [Mo 6 S 8 (PEt 3 ) 6 ] n (n = 1+ to 2-) 21 have been described; while the hexanuclear cluster compounds with edge bridged halide ligands also exhibit extensive redox behaviour, 22-24 and redox pairs such as [Ta 6 Cl 14 (PEt 3 ) 4 ] n+ (n = 0, 1) have been isolated. 25 Up to ten sequential reversible reductions have been reported for the high-nuclearity platinum cluster [Pt 26 (CO) 32 ] n (n = 0 to -10).…”

Computational Methods: Transition Metal Clusters

“…This is observed for [W 6 (µ 6 -C)(µ-Cl) 12 Cl 6 ] 2− for instance. 66 Because the optimal mve count of a face-capped octahedral cluster is also 84, the fused clusters should have a count equal to three times 84 minus twice 42 (mve count of the shared triangular unit). This gives 168 mve.…”