Synthesis and Structures of [Mo12E16(PEt3)10] (E = S,Se)

Dodecanuclcar cluster complexes Mo₁₂S₁₆(PEt₃)₁₀] 1 and Mo₁₂Se₁₆(PEt₃)₁₀] 2 have been prepared by the reactions of Mo₆S₈(PEt₃)₆] with sulfur or Mo₆Se₈(PEt₃)₆] with Cp₂TiSe₅, respectively, in toluene at refluxing temperature. The structures have been determined at 173 K by X-ray crystallography. The compound 1 ·3CHCl₃ crystallizes in the triclinic space group $ {\rm P}\bar 1 $, with a = 14.859(5) Å, b = 15.868(4) Å, c = 14.200(7) Å, α = 100.58(3)°, β = 117.58(3)°, γ = 79.53(2)°, V = 2899(1) ų, and Z = 1. Full-matrix least-squares refinement using 9016 observed reflections (I_o > 2σ(I_o)) gave R = 0.056, and R_w = 0.045. The data for 2 ·2CHCl₃ are: triclinic, $ {\rm P}\bar 1 $, a = 15.737(4) Å, b = 18.763(9) Å, c = 13.062(4) Å, α = 102.45(3)°, β = 128.54(2)°, γ = 69.49(3)°, V = 2825 ų, Z = 1, R = 0.096, and R_w = 0.120 for 5922 reflections (I_o > 2σ(I_o)). The cluster complexes 1 and 2 have two octahedral molybdenum cluster units linked by the rhomboidal intercluster Mo₂(μ₄-E)₂ bonding. The intercluster Mo—Mo distances in 1 are 3.419 Å and 2 3.551 Å. The cyclic voltammetry of 1 and 2 shows two oxidation and two reduction steps separated as large as 380–490 mV. The UV-Vis spectra of the dodecanuclear cluster complexes 1 and 2 have an extra weak band at around 744 nm which is absent in the starting octahedral cluster complexes.