Syntheses, Structures, and Molecular-Orbital Calculations of Chromium Chevrel-Type Cluster Complexes [Cr6E8(PR3)6] (E = S, PR3 = PEt3, PMe3; E = Se, PR3 = PEt3, PMe3, PMe2Ph)

Hexanuclear chromium cluster complexes [Cr6E8(PR3)6] (E = S, PR3 = PEt3, PMe3; E = Se, PR3 = PEt3, PMe3, PMe2Ph) were prepared by the reaction of anhydrous chromium dichloride, a trialkylphosphine, and either NaSH or Na2Se in methanol. The complexes comprised the Cr6 octahedra with eight face-bridging chalcogen atoms and six terminal phosphine ligands. Though the overall ligand arrangements were the same, the symmetry of the central Cr6 octahedra was Oh in PEt3 complexes, but distorted to D3d and D2h in PMe3 and PMe2Ph complexes, respectively. Because of a weakness of the metal–metal interaction, the steric and electronic effect complementarily caused a variation in the chromium octahedra. The electronic effect was analyzed by molecular-orbital calculations using the DV-Xα method.