N—H...S and N—H...O hydrogen bonds: `pure' and `mixed' R²₂(8) patterns in the crystal structures of eight 2-thio­uracil derivatives

The preferred hydrogen-bonding patterns in eight crystal structures of 2-thiouracil derivatives were analysed. In five of the structures, the usual pairs of N—H...S or N—H...O hydrogen bonds are formed, whereas three structures contain `mixed' R²₂(8) patterns with one N—H...S and one N—H...O hydrogen bond.