C-H...pi, pi-pi and C-H...Cl interactions in chloro-substituted Schiff bases and 4-chloro-N-[4-(dimethylamino)benzylidene]aniline.

Molecular packing analyses were carried out on 15 crystal data sets of chloro-substituted Schiff bases, including that of the title compound, C15H15ClN2. C-H...pi and pi-pi interactions play a major role in the molecular self-assembly in the crystal. The former interactions favor molecules assembling into a screw, with a non-centrosymmetric crystal structure. When the molecular dipole is small, pi-pi interactions favor a parallel, but not usually antiparallel, mode of packing. Weak C-H...X hydrogen bonds (X = Cl or Br) and X...X interactions seem to be a secondary driving force in packing. The title molecule takes the trans form and the two benzene rings are twisted around the central linkage in opposite directions. In the crystal structure, molecules interact through C-H...pi and pi-pi interactions, forming a 'dimer' and further forming double chains along [001]. The double chains are extended along [101] through C-H...Cl hydrogen bonds, forming double layers in (010). In the third direction, there are only ordinary, weaker, van der Waals interactions, which explains the crystal habit (i.e. thin plate).