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

In an attempt to investigate the putative S - H center dot center dot center dot 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 center dot center dot center dot N hydrogen bond is negated. The presence of five other varieties of hydrogen bond ( N - H center dot center dot center dot O, N - H center dot center dot center dot S, N - H center dot center dot center dot N, C - H center dot center dot center dot O, C - H center dot center dot center dot 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 center dot center dot center dot O and lowest for C - H center dot center dot center dot S with N - H center dot center dot center dot S, N H center dot center dot center dot N and C - H center dot center dot center dot O forming the middle order.