Five varieties of hydrogen bond in 1-formyl-3-thiosemicarbazide: an electron density study.

In an attempt to investigate the putative S-H...N hydrogen bond, we have studied the title compound, 1-formyl-3-thiosemicarbazide, which was revealed in a CSD search as a crystal structure which might show such an interaction. However, a redetermination of the structure at room temperature and careful analysis showed that the earlier study [Saxena et al. (1991). Acta Cryst. C47, 2374-2376] on which the CSD search was based was in error and that the possibility of an S-H...N hydrogen bond is negated. The presence of five other varieties of hydrogen bond (N-H...O, N-H...S, N-H...N, C-H...O, C-H...S) in the crystal packing prompted us to redirect our efforts and to undertake a study of the charge-density distribution at 90 K. The topological analysis of these five varieties of hydrogen bond was carried out with Bader's quantum theory of ;atoms in molecules' and by applying Koch-Popelier's criteria. The analysis reveals that the hydrogen-bond strength is highest for N-H...O and lowest for C-H...S with N-H...S, N-H...N and C-H...O forming the middle order.