Calculation of crystal and molecular structures of the temperature and pressure polymorphs of para-dichlorobenzene p-C6H4Cl2

Abstract

Crystal and molecular structures of the polymorphic para-dichlorobenzene p-C6H4Cl2 (p-DCB) were investigated by molecular packing analysis with a computed dynamical model. This model includes anisotropic atomic repulsive interactions, molecular deformations, and thermal motions. Several crystalline structures with triclinic P1̄, monoclinic P21/a (and P21/c) symmetry have been found by the calculation. Calculated crystal and molecular parameters agree with data of the three phases β, α, and γ determined by x-ray diffraction between 300–100 K at ambient pressure. At room temperature various crystal structures with orthorhombic Pbca and Abma symmetry calculated in the pressure range of a fourth pressure-induced phase δ are compared with the experimental structure δ0 proposed for this phase. Among them the orthorhombic Abma structure named δs has the lowest energy and enthalpy. It is suggested as a possible structure for the high pressure phase δ.