High-pressurein-situcrystallization, structure and phase transitions in 1,2-dichloroethane

The single crystal of 1,2-dichloroethane, C 2 H 4 Cl 2 was in-situ crystallized in a Merrill-Bassett diamond-anvil cell, and its structure determined at 0.7 GPa and 280 K. The crystals are monoclinic, space group P 2 1 / c . The C 2 H 4 Cl 2 molecules in the s-trans conformation are located at the inversion centers. The —H 2 C—CH 2 —ethylene group is disordered in two sites, with equal occupancies, one rotated by 180° to the other about the Cl⋯Cl axis of the molecule. The crystal cohesion forces have been attributed mainly to Cl⋯Cl intermolecular interactions, and their role in the mechanism of the phase transition at 177 K has been analysed. It was found that the order-disorder phase transition in the structure of 1,2-dichloroethane is associated with the breaking of the Cl⋯Cl intermolecular interactions in the disordered phase. The crystal amorphization under non-homogeneous strain and subsequent transition to a new pressure-induced polymorph at 1.5 GPa has been observed.