Layered structures in proton-transfer compounds of 5-sulfosalicylic acid with the aromatic polyamines 2,6-diaminopyridine and 1,4-phenylenediamine

The crystal structures of two proton-transfer compounds of 3-carboxy-4-hydroxybenzenesulfonic acid (5-sulfosalicylic acid) with the aromatic polyamines 2,6-diaminopyridine [namely 2,6-diaminopyridinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate, C5H8N3+.C7H5O6S-.H2O, (I)] and 1,4-phenylenediamine [namely 1,4-phenylenediaminium 3-carboxylato-4-hydroxybenzenesulfonate, C6H10N2(2+).C7H4O6S2-, (II)] have been determined. Both compounds feature extensively hydrogen-bonded three-dimensional layered polymer structures having significant interlayer pi-pi interactions between the cation and anion species. In (I), the pyridine N atom of the Lewis base is protonated and forms a direct hydrogen-bonding interaction with the water molecule, which together with the two amine groups of the cation and the carboxylic acid group of the anion also give additional interactions with O-atom acceptors of the sulfonate group. In (II), a dianionic species results from deprotonation of both the sulfonic and the carboxylic acid groups, and all available O-atom acceptors interact with all dication donors, which lie about inversion centres.