The Polymorphism of Salicylideneanilines Derivatives with Different Halo-substitution

In order to study the polymorphism of derivatives with different halogen substitutions, four halogen analogs of N-(5′-halosalicylidene)-4-haloaniline (5XY) were prepared. In addition to the 5CC, the other three derivatives were found to exhibit polymorphs with similar color and morphology. The crystal structures were determined, and four derivatives in the same forms showed similar molecular conformation, molecular packing in the unit cell and intermolecular contacts. According to thermal analysis, three derivatives (5CB, 5BC, and 5BB) exhibited a solid-state phase transition from orange to yellow form upon heating, and the transformation was successfully monitored using microscopy and FTIR, whereas the two forms of 5CC could stay stable for a long time, even when heated. Similar phase transition phenomena were observed in solution studies. The research elucidates that polymorphism of derivatives with the same type substituents is very similar.