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 dimersviatwo 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 groupP21/n. The molecular structure of the present monoclinic polymorph is very similar to that of the orthorhombic polymorph (space groupFdd2) studied previously [Roychowdhuryet 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 N2H2ring adopting a butterfly conformation.