Molecular Cocrystals of Aromatic Carboxylic Acids with 1,1-Diethylurea: Synthesis and the Crystal Structures of a Series of Nitro-Substituted Analogues

Abstract

Molecular adducts of 1,1-diethylurea with the nitro-substituted aromatic carboxylic acids 2-nitrobenzoic acid, [(C₇H₅NO₄)(C₅H₁₂N₂O)] (1), 3-nitrobenzoic acid, [(C₇H₅NO₄)(C₅H₁₂N₂O)] (2), 4-nitrobenzoic acid, [(C₇H₅NO₄)₂(C₅H₁₂N₂O)] (3), 3,5-dinitrobenzoic acid, [(C₇H₄N₂O₆)(C₅H₁₂N₂O)] (4), 5-nitrosalicylic acid, [(C₇H₅NO₅)(C₅H₁₂N₂O)] (5) and 3,5-dinitrosalicylic acid, [(C₇H₄N₂O₇)(C₅H₁₂N₂O)] (6), have been prepared and characterized by using infrared spectroscopy, and, in the case of four of these [(1), (4), (5) and (6)], by single-crystal X-ray diffraction methods. In all examples, primary cyclic hydrogen-bonding interactions are found between the amide group of the substituted urea and the carboxylic acid group of the acid, while further peripheral associations result predominantly in simple chain polymeric structures, and in one case [adduct (1)], a cyclic tetramer. The crystal structure of the parent 1,1-diethylurea has also been determined, revealing a cyclic hydrogen-bonded tetramer which forms into a chain polymer by weak hydrogen-bonding associations.