Hydrogen-bonded two- and three-dimensional polymeric structures in the ammonium salts of 3,5-dinitrobenzoic acid, 4-nitrobenzoic acid and 2,4-dichlorobenzoic acid.

The structures of ammonium 3,5-dinitrobenzoate, NH4(+) · C7H3N2O6(-), (I), ammonium 4-nitrobenzoate dihydrate, NH4(+) · C7H4NO4(-) · 2H2O, (II), and ammonium 2,4-dichlorobenzoate hemihydrate, NH4(+) · C7H3Cl2O2(-) · 0.5H2O, (III), have been determined and their hydrogen-bonded structures are described. All three salts form hydrogen-bonded polymeric structures, viz. three-dimensional in (I) and two-dimensional in (II) and (III). With (I), a primary cation-anion cyclic association is formed [graph set R4(3)(10)] through N-H...O hydrogen bonds, involving a carboxylate group with both O atoms contributing to the hydrogen bonds (denoted O,O'-carboxylate) on one side and a carboxylate group with one O atom involved in two hydrogen bonds (denoted O-carboxylate) on the other. Structure extension involves N-H...O hydrogen bonds to both carboxylate and nitro O-atom acceptors. With structure (II), the primary inter-species interactions and structure extension into layers lying parallel to (001) are through conjoined cyclic hydrogen-bonding motifs, viz. R4(3)(10) (one cation, an O,O'-carboxylate group and two water molecules) and centrosymmetric R4(2)(8) (two cations and two water molecules). The structure of (III) also has conjoined R4(3)(10) and centrosymmetric R4(2)(8) motifs in the layered structure but these differ in that the first motif involves one cation, an O,O'-carboxylate group, an O-carboxylate group and one water molecule, and the second motif involves two cations and two O-carboxylate groups. The layers lie parallel to (100). The structures of salt hydrates (II) and (III), displaying two-dimensional layered arrays through conjoined hydrogen-bonded nets, provide further illustration of a previously indicated trend among ammonium salts of carboxylic acids, but the anhydrous three-dimensional structure of (I) is inconsistent with that trend.