Acta Crystallographica Section C

Crystal Structure Communications

Volume 69, Part 1 (January 2013)

organic compounds

Acta Cryst. (2013). C69, 93-100    [ doi:10.1107/S010827011204930X ]

Five pseudopolymorphs of 6-amino-2-thio­uracil: absence of N-H...S hydrogen bonds

W. M. Hützler and M. Bolte

Abstract: In order to study the preferred hydrogen-bonding pattern of 6-amino-2-thio­uracil, C4H5N3OS, (I), crystallization experiments yielded five different pseudopolymorphs of (I), namely the dimethyl­formamide disolvate, C4H5N3OS·2C3H7NO, (Ia), the dimethyl­acetamide monosolvate, C4H5N3OS·C4H9NO, (Ib), the dimethyl­acetamide sesquisolvate, C4H5N3OS·1.5C4H9NO, (Ic), and two different 1-methyl­pyrrolidin-2-one sesquisolvates, C4H5N3OS·1.5C5H9NO, (Id) and (Ie). All structures contain R21(6) N-H...O hydrogen-bond motifs. In the latter four structures, additional R22(8) N-H...O hydrogen-bond motifs are present stabilizing homodimers of (I). No type of hydrogen bond other than N-H...O is observed. According to a search of the Cambridge Structural Database, most 2-thio­uracil derivatives form homodimers stabilized by an R22(8) hydrogen-bonding pattern, with (i) only N-H...O, (ii) only N-H...S or (iii) alternating pairs of N-H...O and N-H...S hydrogen bonds.

Formula: C4H5N3OS·2C3H7NO, C4H5N3OS·C4H9NO, C4H5N3OS·1.5C4H9NO and C4H5N3OS·1.5C5H9NO

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