Conformational polymorphs and solvates of 1-(6-aminopyridin2-yl)-3-phenylthiourea

Abstract

Three conformational polymorphs and two solvates of an asymmetrical N,N'-disubstituted thiourea derivative namely, 1-(6-aminopyridin2-yl)-3-phenylthiourea (PTU) have been reported here. In all the polymorphs and solvates, the PTU molecules self-assemble to dimers in the solid state, via two complementary N-H‧‧‧S bonds resulting in the formation of R22(8)-type of H-bond motif. The two PTU molecules in these dimers interact with each other in a head to tail fashion. Furthermore, the PTU molecule adopts trans, cis- conformation with an intramolecular N-H‧‧‧N interaction in all the crystals. The orientation of the aminophenyl ring with respect to the phenyl ring plays crucial role in the solid state packing of the polymorphs and solvates. Additionally, three polymorphs are distinguishable by C-H‧‧‧π, N-H‧‧‧π and π‧‧‧π interactions. The polymorph PTU-1 crystallizes in P-1 space group with Z'=2, whereas the polymorphs PTU-2 and PTU-3 crystallize in Pbcn and R-3 space group, respectively, with Z'=1. On the other hand, the solvate PTU-DMSO crystallize in P21/c with 1:1 host-guest ratio, and PTU-Morpholine exists in P-1 space group with 2:1 host guest ratio. Hirshfeld surface analysis was carried out to compare the intermolecular interactions in the three polymorphs and two solvates of the title compound. The 2D fingerprint analysis of each of the polymorphs reveals that besides the H‧‧‧H interactions, C‧‧‧H and S‧‧‧H interactions contribute more to the generation of polymorphs. The contribution of C‧‧‧H interactions in both PTU-2 (31.6%) and PTU-3 (32.1%) are much higher than that of any molecule in PTU-1 (19.8% and 23% for Molecule A and B, respectively). Additionally, a tiny amount of π‧‧‧π interaction is observed (C‧‧‧C interaction, 4.5%) in the polymorph PTU-1, which is absent in PTU-2 and PTU-3.