Cocrystals of 6-propyl-2-thio-uracil: N-H⋯O versus N-H⋯S hydrogen bonds

Abstract

In order to investigate the relative stability of N-H⋯O and N-H⋯S hydrogen bonds, we cocrystallized the anti-thyroid drug 6-propyl-2-thio-uracil with two complementary heterocycles. In the cocrystal pyrimidin-2-amine-6-propyl-2-thio-uracil (1/2), C 4H 5N 3·2C 7H 10N 2OS, (I), the base pair is connected by one N-H⋯S and one N-H⋯N hydrogen bond. Homodimers of 6-propyl-2-thio-uracil linked by two N-H⋯S hydrogen bonds are observed in the cocrystal N-(6-acetamido-pyridin-2-yl)acetamide-6-propyl-2- thio-uracil (1/2), C 9H 11N 3O 2· 2C 7H 10N 2OS, (II). The crystal structure of 6-propyl-2-thio-uracil itself, C 7H 10N 2OS, (III), is stabilized by pairwise N-H⋯O and N-H⋯S hydrogen bonds. In all three structures, N-H⋯S hydrogen bonds occur only within R 22(8) patterns, whereas N-H⋯O hydrogen bonds tend to connect the homo-and heterodimers into extended networks. In agreement with related structures, the hydrogen-bonding capability of C=O and C=S groups seems to be comparable. © 2011 International Union of Crystallography.