Molecular Cocrystals of Aromatic Carboxylic Acids with Unsymmetrically Substituted Ureas. The Structures of Phenylurea and the 1 : 1 Adducts of Phenylurea with a Series of Nitro-Substituted Acids

Abstract

The crystal structure of phenylurea (1), [(C₇H₈N₂O)], has been determined and revealed a simple cyclic dimer involving hydrogen bonding between the two nitrogen atoms of one molecule and the oxygen atom of a second molecule. The system is completed by a hydrogen bond between the non-substituted nitrogen atom of a third molecule and the oxygen atom of the second molecule to form a chain polymer. The 1 : 1 molecular adducts of phenylurea with 2-nitrobenzoic acid, [(C₇H₅NO₄)(C₇H₈N₂O)] (2), 3-nitrobenzoic acid, [(C₇H₅NO₄)(C₇H₈N₂O)] (3), 3,5-dinitrobenzoic acid, [(C₇H₄N₂O₆)(C₇H₈N₂O)] (4), 2,4,6-trinitrobenzoic acid, [(C₇H₃N₃O₈)(C₇H₈N₂O)] (5), 5-nitrosalicylic acid, [(C₇H₅NO₅)(C₇H₈N₂O)] (6), and 3,5-dinitrosalicylic acid, [(C₇H₄N₂O₇)(C₇H₈N₂O)] (7) have been prepared and characterized by infrared spectroscopy and, for compounds (2), (4), (5) and (6), by single crystal X-ray diffraction methods. The adduct involving phenylurea and 4-nitrobenzoic acid could not be isolated from this system. In all examples, cyclic hydrogen-bonding interactions are found between the phenylurea and the carboxylic acid groups. All display further peripheral hydrogen bond associations that result in the formation of predominantly simple chain polymeric structures.