Crystal structures of four isomeric hydrogen-bonded co-crystals of 6-methylquinoline with 2-chloro-4-nitrobenzoic acid, 2-chloro-5-nitrobenzoic acid, 3-chloro-2-nitrobenzoic acid and 4-chloro-2-nitrobenzoic acid

Abstract

The structures of the four isomeric compounds of 6-methylquinoline with chloro- and nitro-substituted benzoic acids, C7H4ClNO4·C10H9N, namely, 2-chloro-4-nitrobenzoic acid–6-methylquinoline (1/1), (I), 2-chloro-5-nitrobenzoic acid–6-methylquinoline (1/1), (II), 3-chloro-2-nitrobenzoic acid–6-methylquinoline (1/1), (III), and 4-chloro-2-nitrobenzoic acid–6-methylquinoline (1/1), (IV), have been determined at 185–190 K. In each compound, the acid and base molecules are linked by a short hydrogen bond between a carboxyl O atom and an N atom of the base. The O...N distances are 2.5452 (12), 2.6569 (13), 2.5640 (17) and 2.514 (2) Å, respectively, for compounds (I)–(IV). In the hydrogen-bonded acid–base units of (I), (III) and (IV), the H atoms are each disordered over two positions with O site:N site occupancies of 0.65 (3):0.35 (3), 0.59 (4):0.41 (4) and 0.48 (5):0.52 (5), respectively, for (I), (III) and (IV). The H atom in the hydrogen-bonded unit of (II) is located at the O-atom site. In all of the crystals of (I)–(IV), π–π interactions between the quinoline ring system and the benzene ring of the acid molecule are observed. In addition, a π–π interaction between the benzene rings of adjacent acid molecules and a C—H...O hydrogen bond are observed in the crystal of (I), and C—H...O hydrogen bonds and O...Cl contacts occur in the crystals of (III) and (IV). These intermolecular interactions connect the acid and base molecules, forming a layer structure parallel to thebcplane in (I), a column along thea-axis direction in (II), a layer parallel to theabplane in (III) and a three-dimensional network in (IV). Hirshfeld surfaces for the title compounds mapped overdnormand shape index were generated to visualize the weak intermolecular interactions.