3,5-Dihalo-4-hydroxybenzonitriles: isostructures, polymorphs and solvates.

3,5-Dichloro-4-hydroxybenzonitrile and its solvates with benzene and xylene assemble in chain-like arrangements held together by OH...NC interactions. Two polymorphs each of the corresponding dibromo and diiodo compounds form similar chains which are then bound together by X...X interactions to form approximately planar sheets. These sheets are essentially identical in all four of the bromo and iodo compounds and have approximate p2gg two-dimensional symmetry. These four compounds form an extreme example of two-dimensional isostructuality. The polymorphs differ in the stacking arrangements. One of the Br polymorphs is isostructural with one of the I polymorphs.