An X-ray diffraction study of mesoionic 1-thia-2,3,4-triazolo-5-aminidine and some of its derivatives

X-ray diffraction data are presented for the title mesoionic compound (I), its hydrochloride salt (II) and methylated derivative (III). The crystal of (I) is orthorombic, space group P212121, with cell dimensions: a = 5.857(1) Å, b = 12.494(2) Å, c = 16.328(3) Å, with four molecules per unit cell. The crystal of (II) is monoclinic, space group P21/n, with cell dimensions: a = 5.5720(10) Å, b = 21.5770(4) Å, c = 11.2330(2) Å, beta = 95.15(3)°, with four molecules per unit cell. The crystal of (III) is monoclinic, space group P21/n, with cell dimensions: a = 12.0886(5) Å, b = 7.9103(4), c = 104.29(1) Å, beta = 104.29(1)°, with four molecules per unit cell. Of particular interest is the fact that the C5–N6 bond appears to have a high double bond character in all three of the compounds studied. In addition, it is found that the exocyclic N-phenyl group changes from being in the cis conformation with respect to sulfur in compounds (I) and (III) to the trans conformation in the hydrochloric salt (II).