MOLECULAR CO-CRYSTALS OF CARBOXYLIC-ACIDS .22. THE ADDUCTS OF PYRAZINE-2,3-DICARBOXYLIC ACID WITH 2-AMINOBENZOIC ACID (1 2) AND 3-AMINOBENZOIC ACID (1/1 DIHYDRATE)/

The structures of two molecular adducts of pyrazine-2,3-dicarboxylic a cid (PDCA) with the carboxylic acids 2-aminobenzoic acid (2-ABA), i.e. bis(2-carboxyphenyl-ammonium) 2,3-pyrazinedicarboxylate, [(PDCA)(2-)( 2-ABA(+))(2)], (1), and 3-aminobenzoic acid (3-ABA), i.e. 3-carboxyphe nylammonium hydrogen 2,3-pyrazinedicarboxylate dihydrate, [(PDCA)(3-AB A)(+).2H(2)O], (2), have been determined by X-ray diffraction, In addu ct (1), each carboxylic acid group of PDCA protonates an amino group o f a two 2-ABA molecule. The ion pairs then associate via hydrogen bond ing giving a three-dimensional network structure. In (2), a single pro ton transfer occurs. The protonated amine group of 3-ABA then forms hy drogen bonds with the carboxylate O atoms and the hetero N atom of PDC A as well as with the water molecules, The two 3-ABA molecules also as sociate to form a cyclic hydrogen-bonded dimer. This results in a thre e-dimensional network structure.