CRYSTAL AND MOLECULAR-STRUCTURE OF [ETA-3-ALLYL)DICARBONYLTRIS(METHYL CYANIDE)-MOLYBDENUM(II][BIS(ETA-3-ALLYL)TETRACARBONYL-MU-TRICHLORODIMOLYBDATE(II)] BENZENE (1-1)

The complexes previously reported to be the halogen bridged dimers [MoX(CO)2(η3-C3H5)(MeCN)]2, where X = Cl or Br, have been shown to be [Mo(CO)2(η3-C3H5)(MeCN)3]+[Mo2X3(CO)4(η3-C3H5)2]- in both the solid and solution states. Crystals of the chloro complex grown from benzene contain a solvent molecule and are monoclinic, space group P21/a with cell dimensions a = 16.352(11), b = 13.233(10), c = 16.067(12) Å, β = 97.5(1)°, Z = 4. 2265 independent reflections above background have been measured using a twinned crystal on a diffractometer and refined to R 0.095 using full-matrix least squares. In the cation [Mo(CO)2(η3C3H5)(MeCN)3]+, the metal geometry is best considered as an octahedron with the allyl group [MoC 2.25(4)-2.36(5) Å] occcupying one site and together with two carbonyl groups [MoC 1.99(4), 1.94(4) Å] forming a fac arrangement. The three MeCN groups [MoN 2.22(3), 2.19(3), 2.19(3) Å] complete the coordination sphere. In the anion [Mo2Cl3(η3-C3H5)2(CO)4]-, the two independent molybdenum atoms are each bonded to an allyl group [MoC 2.23(4)-2.38(4) Å] and two carbonyl groups [1.90(4)-1.95(4) Å] in a fac-arrangement. The two metal atoms are bridged by three chlorine atoms [MoCl(trans to allyl)2.52(1) Å; MoCl(trans to carbonyl) 2.58(1)-2.62(1) Å]. Cations, anions and solvent benzene molecules are separated by the usual van der Waals contacts. © 1979.