Descriptions of azoheteroaromatic compounds in their cis-isomeric form in the solid state are almost non-existent. Cis-2,2′-azopyridine is a known compound which structure differentiates from the trans-isomer based on spectroscopic evidence (UV–Vis absorption, 1H, and 13C NMR spectroscopy) and with studies regarding its stability, thermal reversion to the trans-isomer, and dipole moment in solution. However, the structure of this compound in the solid state has been unresolved. Herein, we present the crystal structure of cis-2,2′-azopyridine that forms red prismatic crystals in the monoclinic space group C2/c. The unit cell parameters are: a = 23.485 (4), b = 5.9241 (12), c = 21.656 (4) Å, and V = 2717.1 (9) Å3 with 12 molecules per unit cell. Molecules are arranged as two helical conformers (P and M) with C–N=N–C torsion angles and aromatic ring planes’ angles comparable to those reported for cis-azobenzene.
The rare structural determination of an azoheteroaromatic cis-isomer of 2-azopyridine that was synthesized, isolated and crystallized is presented. X-ray structure analysis reveals that the molecule forms dimeric complexes containing both M- and P-helical conformers as well as infinite stacked columns in the solid state through a combination of C–H⋯N hydrogen bonds, C–H⋯π interactions and lone pair⋯π contacts.
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We wish to thank the Natural Science and Engineering Research Council of Canada, the National Natural Science Foundation of China (No. 21302232), Wuhan Science and Technology Bureau (No. 2015011701011599), Program for Excellent Young Innovative Research Team in the Higher Education Institutions of Hubei Province (No. T201726) for funding this research.