Four polymorphic structures of a symmetric azo dye.

The synthesis and structural characterisation of a symmetric azo dye, ethyl azocinnamate, via single crystal X-ray diffraction led to the discovery of four polymorphic forms. The crystals and their structures were analysed in terms of morphology, conformation, intermolecular interactions and overall crystal packing. This analysis provides insight into their properties, formation and stability. Two distinct conformations were observed, with two representative structures of each. The structures are layered, and were observed to grow as flat, planar crystals with the exception of one, the prismatic habit of which could be attributed to the strong inter-layer interactions unique to this form. The elastic properties of one of the polymorphs was linked to columns of π⋯π interactions along one direction, a feature absent in the more rigid forms. One polymorph with Z' > 1, which crystallises in the space group P21, is analysed in terms of approximate symmetry and is found to be a distorted P21/c structure.