Consistent supra-molecular motifs and different local symmetries in the structures of 2-amino-5-(4-fluoro-phen-yl)-1,3-thia-zole-4-carbaldehyde and 2-amino-5-(4-chloro-phen-yl)-1,3-thia-zole-4-carbaldehyde.

The first title compound, C10H7FN2OS, crystallizes in space group P1 with two independent mol-ecules in the asymmetric unit, which form a dimer with an R 2 2(8) motif through pairwise N-H⋯N hydrogen bonds. In the crystal of (I), N-H⋯O hydrogen bonds bind the dimers into zigzag ribbons running along the [100] direction, generating R 4 4(14) motifs. The second title compound, C10H7ClN2OS (space group I2/a), contains one mol-ecule in the asymmetric unit, which forms a dimer with an R 2 2(8) motif via inversion symmetry. In the extended structure, the mol-ecules form zigzag ribbons in the [100] direction by N-H⋯N and N-H⋯O hydrogen bonds, resulting in consecutive R 4 1(8)R 2 1(5)R 2 2(8)R 2 1(5)R 4 1(8) motifs. The Hirshfeld surface analyses of the compounds (I) and (II) indicates that the most important factors influencing the crystal packing are H⋯H inter-actions [21.1% for mol-ecule A of (I), 20.3% for mol-ecule B of (I) and 21.0% for (II)].