Structural studies of trimeric pyridinium carboxylate carboxylic acid cocrystals

The synthesis and crystal structures of pyridinium 4-nitrobenzoate 4-nitrob enzoic acid (structure 1), 2-vinylpyridinium 4-nitrobenzoate 4-nitrobenzoic acid (structure 2), and 2-vinylpyridinium 3,5-dinitrobenzoate 3,5-dinitrob enzoic acid (structure 3) are described. Despite recrystallization of 1:1 s olutions of pyridine and carboxylic acid, crystals constructed of 1:1:1 pyr idinium carboxylate and carboxylic acid molecules form. These unusual discr ete molecular trimers are linked by N+-H ... O- and O-H ... O hydrogen bond s. The formation of the hydrogen bond patterns for structures 1 to 3 and th e role of pi-stacking on molecular arrangements in these systems are discus sed. (C) 1999 Elsevier Science Ltd.