Acta Cryst. (2013). B69, 405-413 [ doi:10.1107/S2052519213013481 ]
Abstract: We have redetermined the known structures of (i) methylthiourea (MTU) and (ii) 1,1-dimethylthiourea (1,1-DMTU), and investigated the structure of 1,3-dimethylthiourea (1,3-DMTU), which was however severely disordered. We report the structures of crystalline adducts of (iii) MTU with morpholine (1:1), (iv) 1,1-DMTU with 1,4-dioxane (2:1) and (v) 1,3-DMTU with 1,4-dioxane (2:1). Finally, (vi) we determined the structure of tetramethylthiourea (TetMTU). (i) In both independent molecules of MTU, the methyl group is trans to the C=S group across the C-N bond. The two molecules are connected to form an R22(8) dimer by mutual N-HS=C interactions. The packing involves six N-HS=C interactions and is three-dimensional. (ii) The packing of the MTU-morpholine adduct is a layer structure, within which both molecules form linear aggregates parallel to the b axis. (iii) The packing of 1,1-DMTU involves N-HS=C hydrogen bonds forming a corrugated layer structure. (iv) In the 2:1 adduct between 1,1-DMTU and 1,4-dioxane, the DMTU molecule occupies a general position whereas the dioxane molecule lies across an inversion centre. The crystal packing involves chains of alternating 1,1-DMTU R22(8) dimers and dioxanes, both across inversion centres. (v) In the 2:1 adduct between 1,3-DMTU and dioxane, the 1,3-DMTU molecule occupies a general position, while the dioxane molecule lies across an inversion centre. One methyl group of the DMTU is trans and one cis to the sulfur across the corresponding C-N bond. The molecules form chains of alternating 1,3-DMTU R22(8) dimers and dioxanes, both across inversion centres. Crystals of the 2:1 adduct between 1,3-DMTU and morpholine were also obtained, and were isotypic with the dioxane adduct. The morpholine molecule is disordered across the inversion centre. (vi) The molecule of TetMTU displays crystallographic twofold symmetry. Significant distortions reflect the steric pressure between methyl groups trans to sulfur. The packing of TetMTU involves only a weak hydrogen bond, C-HmethylS, which connects the molecules to form layers.
Keywords: hydrogen-bonding patterns; packing; layer structure.
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