Hydrated salts of 3,5-dihydroxybenzoic acid with organic diamines: hydrogen-bonded supramolecular structures in two and three dimensions

Abstract

The trigonally trisubstituted acid 3,5-dihydroxybenzoic acid forms hydrated salt-type adducts with organic diamines. In 1,4-diazabicyclo[2.2.2]octane–3,5-dihydroxybenzoic acid–water (1/1/1) (1), where Z′ = 2 in P21/c, the constitution is [HN(CH2CH2)3N]+·[(HO)2C6H3COO]−·H2O: the anions and the water molecules are linked by six O—H...O hydrogen bonds to form two-dimensional sheets and each cation is linked to a single sheet by one O—H...N and one N—H...O hydrogen bond. Piperazine–3,5-dihydroxybenzoic acid–water (1/2/4) (2) and 1,2-diaminoethane–3,5-dihydroxybenzoic acid–water (1/2/2) (3) are also both salts with constitutions [H2N(CH2CH2)2NH2]2+·2[(HO)2C6H3COO]−·4H2O and [H3NCH2CH2NH3]2+·2[(HO)2C6H3COO]−·2H2O, respectively. Both (2) and (3) have supramolecular structures which are three-dimensional: in (2) the anions and the water molecules are linked by six O—H...O hydrogen bonds to form a three-dimensional framework enclosing large centrosymmetric voids, which contain the cations that are linked to the framework by two N—H...O hydrogen bonds; in (3) the construction of the three-dimensional framework requires the participation of cations, anions and water molecules, which are linked together by four O—H...O and three N—H...O hydrogen bonds.