The crystal structure of a modification of hexaphenylbenzene

Abstract

The structure of one of the polymorphic forms of hexaphenylbenzene, [C. C6H516, has been determined by single-crystal X-ray diffraction work. The crystals are orthorhombic, space group Pna2~ with a = 11080, b=21777, c= 12-553 A. The orientation of the molecule in the asymmetric unit was obtained from the Patterson function, the position by trial and error. The parameters were refined by a block-diagonal least-squares method using 1404 observed intensities recorded with a linear diffractometer. No hydrogen atoms were included in the calculations. The final R value was 0.068. The noncentrosymmetric molecule adopts a propeller configuration with approximate sixfold symmetry. The peripheral rings are not perpendicular to the central ring but are twisted about 25 ° from this position. Bond distances and angles in the benzene rings are normal; the C-C bridge distances vary between 147 and 1.53/~. Standard deviations are 0.013 A and 0.9 ° for bond lengths and angles respectively. All benzene rings are essentially planar. The molecule is highly distorted as the result of out-of-plane bending of the exocyclic bonds. The molecules are packed in pseudo-hexagonal layers parallel to the bc plane.