In the P polymorph of benzanilide or N‐phenyl­benz­amide, C13H11NO, the mol­ecules are linked into simple C(4) chains by N—H⋯O hydrogen bonds. The mol­ecules exhibit orientational disorder, but the donor and acceptor in a given hydrogen bond may occur, independently, in either the major or the minor orientation, such that all four possible N—H⋯O combinations have very similar geometries. The structure of this P polymorph can be related to that of a previously reported C2/c polymorph.

Molecules of 2‐methyl‐4‐nitro­aniline, C7H8N2O2, act as double donors and as double acceptors of N—H⃛O hydrogen bonds [N⃛O 3.117 (3) and 3.239 (3) Å; N—H⃛O 169 and 136°]. The mol­ecules are thereby linked into a three‐dimensional framework.

Three of the nine isomeric N-(nitrobenzylidene)iodoanilines, C13H9IN2O2, have been found, when crystallized from acetone, to yield polymorphs which differ from those obtained upon crystallization from ethanol. In the second polymorph of 2-iodo-N-(2-nitrobenzylidene)aniline, the molecules are disordered across inversion centres in space group C2/c, but there are no direction-specific interactions between the molecules. In the second polymorph of 2-iodo-N-(3-nitrobenzylidene)aniline, the molecules adopt a different conformation from those in the first polymorph, and they are linked into sheets by a combination of a three-centre iodo-nitro interaction and an aromatic pi-pi stacking interaction, both of which are absent from the supramolecular structure of the first polymorph. The second polymorph of 3-iodo-N-(2-nitrobenzylidene)aniline crystallizes with Z' = 2 in space group P2(1), and the molecules are linked into sheets by one C-H...O hydrogen bond and two C-H...pi(arene) hydrogen bonds.

Molecules of the title compound, C14H7FN2O4, are linked by two C-H...O hydrogen bonds [H...O = 2.42 and 2.44 A, C...O = 3.173 (9) and 3.313 (10) A, and C-H...O = 134 and 157 degrees] into deep tripartite sheets, where the central layer is built from hydrogen-bonded R(6)6(24) rings and where the F atoms all lie on the exterior surfaces of the sheets.

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The title compound, C20H20N4O4, crystallizes with two molecules in the asymmetric unit. Each independent mol­ecule exhibits approximate twofold rotation symmetry, but conformational differences between the mol­ecules preclude any higher symmetry.

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Molecules of N,N'-bis(4-nitrobenzylidene)ethane-1,2-diamine, C16H14N4O4, (I), lie across centres of inversion in space group P2(1)/n and are linked into (10-1) sheets by a single C-H...O hydrogen bond [H...O = 2.40 A, C...O = 3.2166 (13) A and C-H...O = 146 degrees ]; these sheets are linked into a three-dimensional array by a single aromatic pi-pi stacking interaction. Molecules of N,N'-bis(4-nitrobenzylidene)propane-1,3-diamine, C17H16N4O4, (II), lie across twofold rotation axes in space group C2/c and are linked into chains of spiro-fused rings by a single C-H...O hydrogen bond [H...O = 2.54 A, C...O = 3.267 (2) A and C-H...O = 130 degrees ]; these chains are linked into sheets by a single aromatic pi-pi stacking interaction.