Supramolecular equivalence of ethynyl, chloro, bromo and iodo groups. A comparison of the crystal structures of some 4-phenoxyanilines

4-(4′-Iodo)phenoxyaniline is isostructural to the corresponding bromo, chloro and ethynyl derivatives in contrast to 4-iodoaniline which is not isostructural to its bromo, chloro and ethynyl counterparts. This difference is rationalised in terms of conditional isomorphism.