Interplay of hydrogen bonds, iodo...nitro interactions and aromatic m stacking interactions in iodo-nitroanilines

Molecules of 2-iodo-5-nitroaniline (I) are linked by N-H...O hydrogen bonds into centrosymmetric dimers and by asymmetric three-centre iodo...nitro interactions into chains, so forming chains of fused centrosymmetric rings: these chains are linked by aromatic pi...pi stacking interactions to form a three-dimensional structure. In the isomeric 4-iodo-2-nitroaniline (II), each of the two independent molecules forms hydrogen-bonded chains that are linked by two-centre iodo ... nitro interactions into sheets of two types, each containing only a single type of molecule: pi...pi stacking interactions are absent. In 2,4-diiodo-3-nitroaniline (III), where the nitro group is almost orthogonal to the aryl ring, a combination of N-H...O hydrogen bonds and two distinct two-centre iodo...nitro interactions links the molecules into a three-dimensional framework that is reinforced by aromatic pi...pi stacking interactions. Bond lengths and conformations are discussed and comparisons are drawn with related compounds.