Two regioisomers of condensed thio-heterocyclic triazine synthesized from 6-phenyl-3-thioxo-2,3,4,5-tetra-hydro-1,2,4-triazin-5-one

In the crystal structure of 6-phenyl-3-thioxo-2,3,4,5-tetra-hydro-1,2,4- triazin-5-one, C₉H₇N₃OS, (I), the 1,2,4-triazine moieties are connected by face-to-face contacts through two kinds of double hydrogen bonds (N - H⋯O and N - H⋯S), which form planar ribbons along the a axis. The ribbons are crosslinked through C - H⋯π interactions between the phenyl rings. The mol-ecular structures of two regioisomeric compounds, namely 6-phenyl-2,3-dihydro-7H-1,3-thia-zolo[3,2-b][1, 2,4]triazin-7-one, C₁₁H₉N₃OS, (II), and 3-phenyl-6,7-di-hydro-4H-1,3-thia-zolo[2,3-c][1,2,4]triazin-4-one, C ₁₁H₉N₃OS, (III), which were prepared by the condensation reaction of (I) with 1,2-dibromo-ethane, have been characterized by X-ray crystallography and spectroscopic studies. The crystal structures of (II) and (III) both show two crystallographically independent mol-ecules. While the two compounds are isomers, the unit-cell parameters and crystal packing are quite different and (II) has a chiral crystal structure.