Disorder in the Crystal Structures of Hexakis(dimethylsilyl)benzene and its Tricarbonyl Chromium, Molybdenum, and Tungsten Complexes

The crystal structures of hexakis(dimethylsilyl)benzene (1) and its tricarbonyl tungsten (2), molybdenum (3) and chromium (4) complexes were determined by X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group P2₁/c with a = 11.196(5)Ǻ, b = 19.675(9)Ǻ, c = 24.447(8)Ǻ, Z = 8, at 175K. The metal complexes 2, 3, 4 are isomorphic; the compounds exhibit trigonal modifications (2t, 3t, 4t), space group R3 or R3, Z = 6. Crystal data: (2t) a = 19.044(5)Ǻ, c = 14.343(4)Ǻ, at 193 K; (3t) a = 19.056(4)Ǻ, c = 14.633(5)Ǻ, at 298 K; (4t) a = 19.047(5)Ǻ, c = 14.144(5)Ǻ, at 193 K. The metal complexes were dimorphic; compounds 2 and 3 exhibit monoclinic modifications (2m, 3m), space group P21 Z = 2. Crystal data: (2m) a = 11.059(4)Ǻ, b = 13.885(4)Ǻ, c = 11.140(3)Ǻ, β = 114.79(3)Ǻ°, at 225 K; (3m) a = 11.020(6)Ǻ, b = 13.838(4)Ǻ, c = 11.099(4)Ǻ, β = 114.54(3)°, at 193 K. Each of the five structures that were solved and refined (1, 2m, 2t, 3m, 4t) exhibit an orientational disorder. The extent of the disordering, measured as the refined occupancy of the minor species, varies for independent molecules within the same asymmetric unit in 1, and between isomorphic structures in the trigonal and monoclinic series of 2, 3, and 4. The disorder was accommodated differently in the trigonal and monoclinic modifications. The metal tricarbonyl units adopt a staggered conformation with respect to the side chains. Substantial out-of-plane deviations (>0.2 Ǻ) of the dimethylsilyl groups were observed in all the structures and arene bond alternations were measured in the metal complexes.