Supramolecular structures in three thiouracil derivatives: 5,6-trimethylene-2-sulfanylidene-1,2-dihydropyrimidin-4(3H)-one, 2-(4-fluorobenzylsulfanyl)-5,6-trimethylenepyrimidin-4(3H)-one and methyl 2-{[2-(4-fluorobenzylsulfanyl)-5,6-trimethylenepyrimidin-4-yl]oxy}acetate.

The mol­ecules of the title compounds, C7H8N2OS, (1), C14H13FN2OS, (2), and C17H17FN2O3S, (3), crystallize in the space groups C2/m, C2/c and Ia, respectively. Compounds (1) and (2), an S-alkyl­ated derivative of (1), consist of only one symmetry-independent mol­ecule, while (3), an O-alkyl­ated derivative of (2), contains two independent mol­ecules in the asymmetric unit. The molecules of (1) sit on crystallographic mirror planes. In the supra­molecular structure of (1), a combination of N—H⋯O and N—H⋯S hydrogen bonds creates a mol­ecular strap with C(6) and R22(8) motifs, which is further stabilized by an S⋯S contact. In the packing of (2), a one-dimensional mol­ecular column is made up of two kinds of dimers. One dimer, with an R22(18) motif, is formed by a pair of C—H⋯O soft hydrogen bonds and the other, with an R22(8) motif, is produced via a pair of N—H⋯O hard hydrogen bonds. In the packing of (3), mol­ecules A and B form two different types of one-dimensional chain by inter­molecular C—H⋯N hydrogen bonds, and by C⋯N and O⋯S contacts, respectively. Two such kinds of chain are connected alternately via inter­chain C—H⋯O hydrogen bonds, giving a two-dimensional sheet. Finally, a three-dimensional supra­molecular structure is formed through weak intersheet C—H⋯F hydrogen bonds. The study of the mol­ecular and supra­molecular structures of thio­uracil derivatives is significant in the development of lipoprotein-associated phospho­lipase A2 inhibitors.