N-H···S and N-H···O hydrogen bonds: 'pure' and 'mixed' R2(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, C7H10N2OS, (I), 5-methoxy-2-thiouracil, C5H6N2O2S, (II), 5-methoxy-2-thiouracil-N,N-dimethylacetamide (1/1), C5H6N2O2S·C4H9NO, (IIa), 5,6-dimethyl-2-thiouracil, C6H8N2OS, (III), 5,6-dimethyl-2-thiouracil-1-methylpyrrolidin-2-one (1/1), C6H8N2OS·C5H9NO, (IIIa), 5,6-dimethyl-2-thiouracil-N,N-dimethylformamide (2/1), 2C6H8N2OS·C3H7NO, (IIIb), 5,6-dimethyl-2-thiouracil-N,N-dimethylacetamide (2/1), 2C6H8N2OS·C4H9NO, (IIIc), and 5,6-dimethyl-2-thiouracil-dimethyl sulfoxide (2/1), 2C6H8N2OS·C2H6OS, (IIId), were analysed. All eight structures contain R(2)(2)(8) patterns. In (II), (IIa), (III) and (IIIa), 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 (IIIb), (IIIc) and (IIId) 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.