Crystal polymorphs of 6-[(phenylcarbamoyl)oxy]hexa-2,4-diyn-1-yl isonicotinate.

The title compound, C19 H14 N2 O4 , was found to have two crystal polymorphs, in which the molecular structures of the diacetylenic compound are broadly similar. The main structural difference between the polymorphs concerns the intermolecular hydrogen-bonding motifs adopted, namely a one-dimensional zigzag polymer linked by N-H...N(py) (py is pyridine) interactions in polymorph I and a centrosymmetric dimeric motif formed by N-H...O=C interactions in polymorph II. The diacetylene cores of the molecules stack along the a and b axes in polymorphs I and II, respectively. It was found that only the molecular arrangement in polymorph II satisfies Baughman's criterion to afford polydiacetylenes (PDAs) by thermal annealing or irradiation with light. This predicted polymerization activity was confirmed by experiment.