Crystal structures of an isomeric pair of 3-methylthio-5-amino-1,2,4-triazoles

Abstract

The structures of an isomeric pair: 1-[2-(2,6-dichlorophenoxy)-ethyl]-3-methylthio-5-amino-1 H-1,2,4-triazole (IV) and 2-[2-(2,6-dichlorophenoxy)-ethyl]-3-methylthio-5-amino-2 H-1,2,4-triazole (V) have been established by X-ray crystallography from diffractometer data. Crystals of IV are monoclinic, space group P2 1/ c with a = 11.220(1), b = 10.005(3), c = 12.784(3) Å, β = 91.99(1)°, Z = 4, D c = 1.478 g cm −3. Crystals of V are orthorhombic, space group Pbca with a = 7.618(2), b = 14.289(4), c = 26.494(7) Å, Z = 8, D c = 1.470 g cm −3. The structures determined by direct methods were refined to R = 0.060 for 1931 reflections of IV and R = 0.061 for 1315 reflections of V. The X-ray analysis corroborated the structures assigned to the isomeric pair on the basis of proton coupled 13C-NMR spectra. The features (i.e. the sequence of the endocyclic bond angle magnitudes) of the planar s-triazole rings are governed by the same rules reported recently by Kálmán and Argay [J. Mol. Struct., 102 (1983) 391] discussing the structures of the related I, II and III compounds. In contrast to I, II, III and IV the S(6)C(7) bond of V is almost perpendicular to the best plane of the s-triazole ring C(7)S(6)C(3)N(4) = −79.0(7)°. This unusual orientation of the S-methyl bond is created by the steric hindrance of the very same vicinal 2-ethyl (C(9)H 2C(10)H 2) moiety once within the molecule V and the second time as the part of a symmetry equivalent molecule at a distance of − a (7.618 Å). These molecules are fixed together by two infinite helices of hydrogen bonds formed around the screw axis 2, ( X, 1/4, 1/2) via an intermediate V molecule at ( x − 1/2, 1/2 − y, 1 − z).