The Crystal and Molecular Structure of Penta-P-tolylantimony, (p-CH3C6H4)5Sb

Abstract

Penta-p-tolylantimony crystals are monoclinic, space group P21/c, with a = 14.545(5), b = 4(6), c = 19.754(8) Å, β = 122.88(4)°, and Z = 4. The structure was solved by the standard heavy-atom method and anisotropic refinement on 1677 independent observed reflections led to a conventional R factor of 0.051. Unlike pentaphenylantimony, which is known to exist as square pyramidal molecules in the crystal, the corresponding penta-p-tolyl derivative exhibits the more common trigonal bipyramid structure. The Sb—C equatorial bond length average, 2.16 Å, is significantly shorter than the axial average, 2.26 Å. Two of the C—Sb—C bond angles in the equatorial plane (113, 130°) differ considerably from 120°, but the other angles around antimony are normal. Packing forces appear to play a determining role in the structures observed for penta-aryl derivatives of antimony in the solid state.