Mechanochemical synthesis ofN-salicylideneaniline: thermosalient effect of polymorphic crystals

Abstract

Polymorphs of the dichloro derivative ofN-salicylideneaniline exhibit mechanical responses such as jumping (Forms I and III) and exploding (Form II) in its three polymorphs. The molecules are connectedviathe amide N—H...O dimer synthon and C—Cl...O halogen bond in the three crystal structures. A fourth high-temperature Form IV was confirmed by variable-temperature single-crystal X-ray diffraction at 180°C. The behaviour of jumping exhibited by the polymorphic crystals of Forms I and III is due to the layered sheet morphology and the transmission of thermal stress in a single direction, compared with the corrugated sheet structure of Form II such that heat dissipation is more isotropic causing blasting. The role of weak C—Cl...O interactions in the thermal response of molecular crystals is discussed.