Interactions of aromatic carboxylic acids with 8-aminoquinoline: Synthesis and the crystal structures of the proton-transfer compounds of 8-aminoquinoline with nitro-substituted benzoic acids

Proton-transfer compounds of 8-aminoquinoline with the nitro-substituted aromatic carboxylic acids 3-nitrobenzoic acid, [(C₉H₉N₂⁺)(C₇ H₄NO₄^-)] (1), 4-nitrobenzoic acid, [(C₉H₉N₂⁺) (C₇H₅NO₄)] (2), 3, 5-dinitrobenzoic acid, [(C₉H₉N₂⁺)(C₇ H₃N₂O₆^-)] (3), 5-nitrosalicylic acid, [(C₉H₉N₂⁺) (C₇H₄NO₅^-)] (4) and 3, 5-dinitrosalicylic acid, [(C₉H₉N₂⁺) (C₇H₃N₂O₇^-)] (5) have been prepared and characterized by using both infrared spectroscopy and single-crystal X-ray diffraction methods [(1) (4) and (5)]. In all compounds, protonation of the quinoline nitrogen occurs together with primary hydrogen-bonding interactions involving this group and the carboxylate group of the acid, while further peripheral associations result predominantly in simple chain polymeric structures. The attempted preparation of the adduct with 2, 4, 6-trinitrobenzoic acid gave the unstable, neutral, essentially 1:1 adduct with the decarboxylation product 1, 3, 5-trinitrobenzene, the X-ray crystal structure of which indicates the stoichiometry [(C₉H₈N₂)_0.6(C₆ H₃N₃O₆)_0.8] (6).