Interactions of Aromatic Carboxylic Acids with Quinolin-8-ol (Oxine): Synthesis and the Crystal Structures of the Proton-Transfer Compounds with the Nitro-Substituted Benzoic Acids

Abstract

Proton-transfer compounds of quinolin-8-ol (oxine) with the nitro-substituted aromatic carboxylic acids 2-nitrobenzoic acid, [(C₉H₈NO⁺)(C₇H₄NO₄^–)·H₂O] (1), 3-nitrobenzoic acid, [(C₉H₈NO⁺)(C₇H₄NO₄)^–] (2), 4-nitrobenzoic acid, [(C₉H₈NO+)(C₇H₄NO₄^–)(C₇H₅NO₄)] (3), 3,5-dinitrobenzoic acid, [(C₉H₈NO⁺)₂(C₇H₃N₂O₆^–)₂·3H₂O] (4), 5-nitrosalicylic acid, [(C₉H₈NO⁺) (C₇H₄NO₅^–)] (5) and 3,5-dinitrosalicylic acid, [(C₉H₈NO⁺)(C₇H₃N₂O₇^–)] (6) have been prepared and characterized by using both infrared spectroscopy and single-crystal X-ray diffraction methods [(3), (4) and (6)]. 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, in the case of the trihydrate (4), also involving the water molecules, result predominantly in simple chain polymeric structures.