Hydrogen bonding in two ammonium salts of 5-sulfosalicylic acid: ammonium 3-carboxy-4-hydroxybenzenesulfonate monohydrate and triammonium 3-carboxy-4-hydroxybenzenesulfonate 3-carboxylato-4-hydroxybenzenesulfonate.

The structures of two ammonium salts of 3-carboxy-4-hydroxybenzenesulfonic acid (5-sulfosalicylic acid, 5-SSA) have been determined at 200 K. In the 1:1 hydrated salt, ammonium 3-carboxy-4-hydroxybenzenesulfonate monohydrate, NH4(+)·C7H5O6S(-)·H2O, (I), the 5-SSA(-) monoanions give two types of head-to-tail laterally linked cyclic hydrogen-bonding associations, both with graph-set R4(4)(20). The first involves both carboxylic acid O-H···O(water) and water O-H···O(sulfonate) hydrogen bonds at one end, and ammonium N-H···O(sulfonate) and N-H···O(carboxy) hydrogen bonds at the other. The second association is centrosymmetric, with end linkages through water O-H···O(sulfonate) hydrogen bonds. These conjoined units form stacks down c and are extended into a three-dimensional framework structure through N-H···O and water O-H···O hydrogen bonds to sulfonate O-atom acceptors. Anhydrous triammonium 3-carboxy-4-hydroxybenzenesulfonate 3-carboxylato-4-hydroxybenzenesulfonate, 3NH4(+)·C7H4O6S(2-)·C7H5O6S(-), (II), is unusual, having both dianionic 5-SSA(2-) and monoanionic 5-SSA(-) species. These are linked by a carboxylic acid O-H···O hydrogen bond and, together with the three ammonium cations (two on general sites and the third comprising two independent half-cations lying on crystallographic twofold rotation axes), give a pseudo-centrosymmetric asymmetric unit. Cation-anion hydrogen bonding within this layered unit involves a cyclic R3(3)(8) association which, together with extensive peripheral N-H···O hydrogen bonding involving both sulfonate and carboxy/carboxylate acceptors, gives a three-dimensional framework structure. This work further demonstrates the utility of the 5-SSA(-) monoanion for the generation of stable hydrogen-bonded crystalline materials, and provides the structure of a dianionic 5-SSA(2-) species of which there are only a few examples in the crystallographic literature.