High pressure solid phases of benzene .3. Molecular packing analysis of the crystalline structures of C6H6

With a computer simulated mechanical-model for molecular packing analysis, the reconstitution and identification of the intermediate pressure-induced phase II of solid benzene C6H6 at 293 K, has been undertaken. The atom-atom intermolecular potential of the Buckingham type was generalized to account for short interatomic distances, especially under pressure. The model includes thermal motion and molecular deformation effects. Various crystal structures calculated in the pressure range of phase II and checked by their reticular distances and structure factors, are compared with the structure IIo proposed for this phase. Among them two possible monoclinic structures IIc and IIc' have been evidenced by the calculation. Structure IIc has energy and enthalpy levels lower than that of phases I-c and IIIc, in the pressure range 0.5 < P < 1.0 GPa. This allows to suggest this stable monoclinic structure IIc for the real structure of the experimentally observed phase II. This structure IIc corresponds to the structure previously determined as metastable by Dzyabchenko and Bazilevskii [J. Struct. Chem. 26, 553 (1985)]. (C) 1998 American Institute of Physics.