Supramolecular diversity in solid-state architecture formed between the 1-(diaminomethylene)thiourea and citric acid

Abstract

Three different single crystals formed between the 1-(diaminomethylene)thiourea and citric acid from water solution depending on the concentration and the molar composition of 1-(diaminomethylene)thiourea to citric acid, i.e. 1-(diaminomethylene)thiouron-1-ium citrate monohydrate (1), tris(1-(diaminomethylene)thiouron-1-ium) citrate (2) and tris(1-(diaminomethylene)thiouron-1-ium) citrate monohydrate (3), were obtained. X-ray single crystal diffraction technique was used for the analysis of the diversity in supramolecular arrangement between the units constituting the crystals. Compound 1 and 3 crystallize in the centrosymmetric space groups (1 in P-1) and 3 in P21/c) whereas compound 2 crystallises in non-centrosymmetric space group P212121. As show the X-ray single crystal analysis the conformation of the 1-(diaminomethylene)-thiouron-1-ium cation in each of studied crystals is not strictly planar, but twisted with the angle of 3.5 (1)o in 1, 4.8 (1) to 13.4 (1)o in 2 and 2.1 (1) to 8.7 (1)o in 3. The flexible carbon chain of the citrate (3-) anion exhibits conformational disorder in 3, whereas the citrate (3-) anion in 2 as well as the citrate (−) mono anion in 1 are ordered. The interaction between the units constituting the crystals including the NH⋯O and OH⋯O hydrogen bonds determine the supramolecular diversity in solid. Hirshfeld surface and the analysis of 2D fingerprint plots are used for illustrate both qualitatively and quantitatively interactions between the units governing the supramolecular assemblies. The compounds were also characterised by vibrational spectroscopy. The vibrational assignment have been supported by the isotopic frequency shift. Within the 1–3 compounds only compound 2 crystallises in non-centrosymmetric space group therefore for it the SHG was measured.