Two concomitant polymorphs of N,N'-bis[4-(diethylamino)phenyl]terephthaldiamide.

The title compound, C(28)H(34)N(4)O(2), crystallizes simultaneously as a monoclinic, (Im), and a (twinned) triclinic polymorph, (It), from d(6)-dimethyl sulfoxide. Polymorph (It) (P-1, Z = 1) displays the standard ;ladder' packing for this group of compounds, with neighbouring inversion-symmetric molecules related by translation and connected by hydrogen bonds of the form N-H...O=C. Polymorph (Im) (Cc, Z = 4) has no imposed symmetry; there are three independent hydrogen bonds, one classical N-H...O=C and a bifurcated system with N-H...O=C augmented by a short C-H...O=C interaction. Each molecule is thereby linked to four neighbouring molecules, two lower and two higher, so that a crosslinked three-dimensional pattern is formed rather than the standard ladder.