Structural aspects and properties of salt and inclusion compounds of 8-hydroxyquinoline based amides

Abstract

The structural aspects of two amide containing isoquinoline derivatives namely N-cyclohexyl-2-(quinolin-8-yloxy) acetamide (1) and N-(2,6-dimethylphenyl)-2-(quinolin-8-yloxy) acetamide (2) are studied. On treatment with mineral acids such as sulfuric acid, hydrochloric or phosphoric acid N-cyclohexyl-2-(quinolin-8-yloxy) acetamide forms gels whereas on treatment with nitric acid it forms crystalline solid. Acids having non-planar anions facilitate the gel formation and the acids having planar anion such as nitrate and carboxylate were not suitable for gelation of 2. N-(2,6-Dimethylphenyl)-2-(quinolin-8-yloxy) acetamide forms crystalline salts on treatment with mineral acids. The crystal structure of compounds 1, 2 and two salts are reported. Compound 2 forms 2 : 1 host–guest complexes with 1,4-dihydroxybenzene as well as with 1,5-dihydroxynaphthalene. The crystal structures of both compounds are reported. These host–guest complexes have much stronger fluorescence emission at lower wavelength than the parent compound, however, the protonated state of compound 2 is not fluorescence active. The compound 1 on protonation shows fluorescence at much higher wavelength than the parent compound, whereas compound 1 on interaction with 1,4-dihydroxybenzene fluorescence occurs at a lower wavelength. The crystal structure of N-[3-(4-methoxy-phenyl)propyl]-2-(quinolin-8-yloxy)acetamide is determined and found to have parallel sheet structure.