Solvent influence on the crystal packing of 6-aminothiocytosine

The crystal structures of 6-aminothiocytosine (systematic name: 4,6-diamino-1,2-dihydropyrimidine-2-thione, DAPMT, C₄H₆N₄S), its hemihydrate (0.5H₂O) and its dimethylformamide (DMF, C₃H₇NO) monosolvate were compared, and the influence of the type of solvent on the supramolecular motifs was analysed. In all three crystal structures, there are two symmetry-independent molecules (A and B), and these molecules are connected by three relatively short and directional hydrogen bonds to form chains of alternating A and B molecules. A further organization of these chains is dependent on the nature of the solvent molecule. In the unsolvated form, two orientations of the neighbouring chains are observed, and similar motifs - but only one per structure - can be observed in the solvated structures. These two different motifs can be connected by two different kinds of contacts, i.e. either π-π (hemihydrate) or staple-supported S...S (DMF). In the crystal structures, the O atoms of the solvent molecules are double acceptors of the same type of hydrogen bonds and bind the chains of DAPMT molecules into different motifs (dimeric or infinite chains). A Hirshfeld fingerprint analysis was used for visualization and additional interpretation of these results.