Synthesis and crystal structure of ethyl 2-(1,3-benzo-thia-zol-2-yl)-1-oxo-1H-pyrido[2,1-b][1,3]benzo-thia-zole-4-carboxyl-ate.

The mol-ecule of the title compound, C21H14N2O3S2, is approximately planar except for the terminal carbon atom of the ethyl group. The planarity is promoted by two short intra-molecular S⋯O=C contacts and one intra-molecular 'weak' C-H⋯O=C hydrogen bond. The two thia-zole rings show some appreciable differences in bond lengths and angles, associated with their different annelation patterns. The mol-ecular packing involves one 'weak' hydrogen bond of the type C-H⋯O=C, which links the mol-ecules in zigzag chains via a 21 screw axis along [010]. Additionally, 'stacked' pairs of mol-ecules, necessarily with parallel ring systems, are related by an inversion operator, and two π contacts C-H⋯π and C=O⋯π are observed.