Ethylenediammonium bis(3,4-dihydroxybenzoate) monohydrate

In the title compound, C2H10N2 2+·2C7H5O4 −·H2O, the cation lies on a centre of symmetry. The crystal structure is stabilized by various intermolecular O—H⋯O and N—H⋯O hydrogen bonds, and by weak π–π stacking interactions with centroid–centroid distances between symmetry-related benzene rings ranging from 3.5249 (13) to 3.7566 (14) Å.

In the title compound, C 2 H 10 N 2 2+ Á2C 7 H 5 O 4 À ÁH 2 O, the cation lies on a centre of symmetry. The crystal structure is stabilized by various intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, and by weakstacking interactions with centroid-centroid distances between symmetry-related benzene rings ranging from 3.5249 (13) to 3.7566 (14) Å .
The author acknowledges South China Normal University for supporting this work.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SU2221).

Comment
Protocatechuic acid (3,4-dihydroxybenzoic acid) is one of the main secondary metabolites in the plant kingdom . Significantly, it has been found that protocatechuic acid and its derivatives possess diverse pharmacological activities such as, antioxidant, antiapoptosis, anticarcinogen, anticoagulatory and antiinflammatory Lin et al., 2009;Tseng et al., 1998;Yip et al., 2006). Herein, we report on the molecular and crystal structure of the title compound.
In the asymmetric unit of the title compound, illustrated in Fig. 1, there are two half protonated ethylenediammonium cations located about inversion centers, two singly deprotonated 3,4-dihydroxybenzoate anions, and one water molecule of crystallization. The bond distances and angles in the title compound are normal (Mazurek et al., 2007;Xu et al., 2008).

Experimental
A solution of ethylenediamine (1 mmol in 0.2 ml water) was added dropwise to a solution of protocatechuic acid (2 mmol) in acetonitrile (15 ml), and the mixture was stirred for 30 min at RT. After several days colourless block-like crystals, suitable for X-ray diffraction analysis, were obtained by slow evaporation of the solution.

Refinement
The water molecule H-atoms were located in difference Fourier maps and were refined distance restraints of O-H = 0.86 Å and U iso (H) = 1.5U eq (O). All other H atoms were positioned geometrically and refined as riding: N-H = 0.89 Å, O-H = 0.82 Å, and C-H = 0.93 and 0.97 Å for CH and CH 2 H-atoms, respectively, with U iso (H) = k × U eq (parent N, O or C-atom), with k = 1.2 for CH and CH 2 H-atoms, and k = 1.5 for the NH 3 + and OH H-atoms.
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound showing the atomic-numbering scheme and displacement ellipsoids drawn at the 30% probability level. Symmetry codes:  Table 1 for details).