Abstract

The structures of the four isomeric compounds of 6-methyl-quinoline with chloro- and nitro-substituted benzoic acids, C7H4ClNO4·C10H9N, namely, 2-chloro-4-nitro-benzoic acid-6-methyl-quinoline (1/1), (I), 2-chloro-5-nitro-benzoic acid-6-methyl-quinoline (1/1), (II), 3-chloro-2-nitro-benzoic acid-6-methyl-quinoline (1/1), (III), and 4-chloro-2-nitro-benzoic acid-6-methyl-quinoline (1/1), (IV), have been determined at 185-190 K. In each compound, the acid and base mol-ecules 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 inter-actions between the quinoline ring system and the benzene ring of the acid mol-ecule are observed. In addition, a π-π inter-action between the benzene rings of adjacent acid mol-ecules 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 inter-molecular inter-actions connect the acid and base mol-ecules, forming a layer structure parallel to the bc plane in (I), a column along the a-axis direction in (II), a layer parallel to the ab plane in (III) and a three-dimensional network in (IV). Hirshfeld surfaces for the title compounds mapped over d norm and shape index were generated to visualize the weak inter-molecular inter-actions.

Highlights

  • Crystal structures of four isomeric hydrogenbonded 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

  • A – interaction between the benzene rings of adjacent acid molecules and a C—HÁ Á ÁO hydrogen bond are observed in the crystal of (I), and C—HÁ Á ÁO hydrogen bonds and OÁ Á ÁCl contacts occur in the crystals of (III) and (IV)

  • In our ongoing study on crystal structures of the system of quinoline derivatives–chloro- and nitro-substituted benzoic acids, we have shown that three compounds of quinoline with 3-chloro-2-nitrobenzoic acid, 4-chloro-2-nitrobenzoic acid and 5-chloro-2-nitrobenzoic acid, the ÁpKa [pKa(base) À pKa(acid)] values of which are 3.08, 2.93 and 3.04, respectively, have a short double-well O—HÁ Á ÁN/ OÁ Á ÁH—N hydrogen bond between the carboxy O atom and the aromatic N atom (Gotoh & Ishida, 2009)

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Summary

Chemical context

Properties of hydrogen bonds formed between organic acids and organic bases depend on the pKa values of the acids and bases as well as intermolecular interactions in the crystals. The benzene ring makes dihedral angles of 29.36 (12) and 8.24 (11), respectively, with the carboxy group and the nitro group (O3/N1/ O4). Similar to (I), the quinoline ring system (N2/C8–C16) in the hydrogen-bonded acid–base unit of (II) makes dihedral angles of 2.15 (4) and 24.51 (15), respectively, with the benzene ring and the carboxy group. In the acid–base unit, the quinoline ring system and the benzene ring of the acid are slightly twisted to each other with a dihedral angle of 14.50 (5). Compound (IV) crystallizes in the non-centrosymmetric space group Cc. In the acid–base unit, the quinoline ring system and the benzene ring of the acid are twisted to each other with a dihedral angle of 30.39 (9). The benzene ring makes dihedral angles of 16.4 (3) and 74.4 (3), respectively, with the carboxy group and the nitro group

Supramolecular features
Database survey
Synthesis and crystallization
Refinement
H15 C16 C17 H17A H17B H17C
H14 C15 H15 C16 C17 H17A H17B H17C H1
C15 H15 C16 C17 H17A H17B H17C

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