Hydrogen bonding in crystal engineering: Two-dimensional layers of hydrogen L-malate anions

Hydrogen L-malate anions can be utilized in the crystal engineering of ionic materials as a means of providing structural consistency and rigidity by creating infinite anionic layers held together by directional O-H ... O hydrogen bonds. The syntheses and crystal structures of three new organic hydrogen L-malate salts, [AH][Hmal], are described (where A = (4-methyl)benzylamine, (4-chloro)benzylamine and (3-chloro)benzylamine). In each case, the anions create extended architectures (infinite layers) via O-H ... O interactions. Each cation is then attached to one side of the anionic layer via three N-H ... O interactions. The layers are stacked in an AABBAABB... fashion with both anionic and cationic sheets arranged in pairs throughout each crystal. The structural influence of the cations, and the importance of the directionality and selectivity of hydrogen bonds in the construction of extended ''building blocks'', is discussed.