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

The preferred hydrogen‐bonding patterns in the crystal structures of 5‐propyl‐2‐thiouracil, C 7 H 10 N 2 OS, (I), 5‐methoxy‐2‐thiouracil, C 5 H 6 N 2 O 2 S, (II), 5‐methoxy‐2‐thiouracil– N , N ‐dimethylacetamide (1/1), C 5 H 6 N 2 O 2 S·C 4 H 9 NO, (II a ), 5,6‐dimethyl‐2‐thiouracil, C 6 H 8 N 2 OS, (III), 5,6‐dimethyl‐2‐thiouracil–1‐methylpyrrolidin‐2‐one (1/1), C 6 H 8 N 2 OS·C 5 H 9 NO, (III a ), 5,6‐dimethyl‐2‐thiouracil– N , N ‐dimethylformamide (2/1), 2C 6 H 8 N 2 OS·C 3 H 7 NO, (III b ), 5,6‐dimethyl‐2‐thiouracil– N , N ‐dimethylacetamide (2/1), 2C 6 H 8 N 2 OS·C 4 H 9 NO, (III c ), and 5,6‐dimethyl‐2‐thiouracil–dimethyl sulfoxide (2/1), 2C 6 H 8 N 2 OS·C 2 H 6 OS, (III d ), were analysed. All eight structures contain R 2 2 (8) patterns. In (II), (II a ), (III) and (III a ), they are formed by two N—H...S hydrogen bonds, and in (I) by alternating pairs of N—H...S and N—H...O hydrogen bonds. In contrast, the structures of (III b ), (III c ) and (III d ) contain `mixed' R 2 2 (8) patterns with one N—H...S and one N—H...O hydrogen bond, as well as R 2 2 (8) motifs with two N—H...O hydrogen bonds.