Synthesis and crystal structures of two racemic 2-heteroaryl-3-phenyl-2,3-di-hydro-4 H -pyrido[3,2- e ][1,3]thia-zin-4-ones.

3-Phenyl-2-(thio-phen-3-yl)-2,3-di-hydro-4 H -pyrido[3,2- e ][1,3]thia-zin-4-one (C 17 H 12 N 2 OS 2 , 1 ) and 2-(1 H -indol-3-yl)-3-phenyl-2,3-di-hydro-4 H -pyrido[3,2- e ][1,3]thia-zin-4-one 0.438-hydrate (C 21 H 15 N 3 OS·0.438H 2 O, 2 ) crystallize in space groups P 2 1 / n and C 2/ c , respectively. The asymmetric unit in each case is comprised of two parent mol-ecules, albeit of mixed chirality in the case of 1 and of similar chirality in 2 with the enanti-omers occupying the neighboring asymmetric units. Structure 2 also has water mol-ecules (partial occupancies) that form continuous channels along the b - axis direction. The thia-zine rings in both structures exhibit an envelope conformation. Inter-molecular inter-actions in 1 are defined only by C-H⋯O and C-H⋯N hydrogen bonds between crystallographically independent mol-ecules. In 2 , hydrogen bonds of the type N-H⋯O between independent mol-ecules and C-H⋯N(π) type, and π-π stacking inter-actions between the pyridine rings of symmetry-related mol-ecules are observed.