Supramolecular architecture formed between amidinothiourea and 2-pyridinecarboxylic acid

Abstract

The single crystals of 1-(diaminomethylene)thiouron-1-ium 2-pyridinecarboxylate, (C2H7N4S)-(C5NH4COO), (1) suitable for the X-ray analysis were grown using a solution growth technique room temperature. Recrystallization of 1 in heavy water (three-times) yield respective deuterated analogue, (C2D7N4S) (C5NH4COO), (1d). The X-ray analyses show that both, protonated and deuterated, compounds crystallize in the same crystal system with quite similar lattice parameters. X-ray analysis on a single crystal of 1 measured at 100 K and RT showed that no structural phase changes were observed between RT and 100 K. At both temperatures, crystal 1 belongs to the centrosymmetric space group of the triclinic system with two molecules in an asymmetric unit. In both molecules of the asymmetric unit the opposite charged units interact each other via the same R22(8) hydrogen bonding graph that is formed by donation of the amine groups linked to the same carbon atom to both oxygen atoms of the COO– of the 2-pyridinecarboxylate anions. The 1-(diaminomethylene)thiouron-1-ium 2-pyridinecarboxylate units are interact each other via additional N–H…O and N–H…N hydrogen bonds formed between these independent hydrogen bonded R22(8) units forming layers parallel to (001) crystallographic plane. The interactions between layers is significantly weaker than within the layers since the layers interact via much weaker NH…S hydrogen bonds. Thus the (001) crystallographic plane is a cleave plane of the crystals 1. Hirshfeld surface and the analysis of 2D fingerprint plots are illustrating both quantitatively and qualitatively interactions governing the supramolecular assemblies. The compound was also characterised by the FT-IR and Raman spectroscopy. Assignment of the vibrational bands have been supported by the DFT calculations and the isotropic frequency shift.