HYDROGEN-BONDED LAYERS OF HYDROGEN MALATE ANIONS - A FRAMEWORK FOR CRYSTAL ENGINEERING

The syntheses and crystal structures of 3-hydroxy-6-methylpyridinium hydrogen L-malate (1), benzimidazolium hydrogen L-malate (2), 3-hydroxypyridinium hydrogen L-malate (3), and (2-chlorobenzyl)ammonium hydrogen L-malate (4) are described; In every case, the anions create infinite layers through two intermolecular O-H...O hydrogen bonds. In 1 and 3, the cations provide a cross-link between adjacent anionic layers, whereas in 2 and 4, the cations are hydrogen bonded to chains within the same layer. Despite;the structural and chemical differences between the cations and the way in which they are attached to the anions, the infinite layer prevails in each compound. This illustrates that hydrogen L-malate anions may be utilized in crystal engineering as a dependable building block, ''scaffolding'', for two-dimensional structural frameworks in the solid state. The importance of the selectivity and directionality of the hydrogen bonds, and the influence of the cations on the geometry of individual anions and of the detailed crystal packing within these structures, is also discussed.