Crystal structure of 8-hydroxyquinoline: A new monoclinic polymorph

Abstract

In an attempt to grow 8-hydroxyquinoline-acetaminophen co-crystals from equimolar amounts of conformers in a chloroform-ethanol solvent mixture at room temperature, the title compound, C9H7NO, was obtained. The molecule is planar, with the hydroxy H atom forming an intramolecular O - H⋯N hydrogen bond. In the crystal, molecules form centrosymmetric dimers via two O - H⋯N hydrogen bonds. Thus, the hydroxy H atoms are involved in bifurcated O - H⋯N hydrogen bonds, leading to the formation of a central planar four-membered N2H2ring. The dimers are bound by intermolecular π-π stacking [the shortest C⋯C distance is 3.2997 (17) Å] and C - H⋯π interactions into a three-dimensional framework. The crystal grown represents a new monoclinic polymorph in the space group P21/n. The molecular structure of the present monoclinic polymorph is very similar to that of the orthorhombic polymorph (space group Fdd2) studied previously [Roychowdhury et al. (1978). Acta Cryst. B34, 1047-1048; Banerjee & Saha (1986). Acta Cryst. C42, 1408-1411]. The structures of the two polymorphs are distinguished by the different geometries of the hydrogen-bonded dimers, which in the crystal of the orthorhombic polymorph possess twofold axis symmetry, with the central N2H2 ring adopting a butterfly conformation.