3,3′-(Piperazine-1,4-diium-1,4-diyl)dipropionate dihydrate

During the recrystallization of 3-[4-(2-carboxyethyl)piperazin-1-yl]propionic acid, the carboxylic acid H atoms were transferred to the piperazine N atoms, forming the title compound, C10H18N2O4·2H2O, in which the zwitterion lies about an inversion center. In the crystal, bifurcated N—H⋯(O,O) hydrogen bonds connect the zwitterions into a two-dimensional framework parallel to (-102) forming R 4 4(30) rings. O—H⋯O hydrogen bonds involving the solvent water molecules connect the two-dimensional framework into a three-dimensional network. In addition, weak C—H⋯O hydrogen bonds are observed.

During the recrystallization of 3-[4-(2-carboxyethyl)piperazin-1-yl]propionic acid, the carboxylic acid H atoms were transferred to the piperazine N atoms, forming the title compound, C 10 H 18 N 2 O 4 Á2H 2 O, in which the zwitterion lies about an inversion center. In the crystal, bifurcated N-HÁ Á Á(O,O) hydrogen bonds connect the zwitterions into a twodimensional framework parallel to (102) forming R 4 4 (30) rings. O-HÁ Á ÁO hydrogen bonds involving the solvent water molecules connect the two-dimensional framework into a three-dimensional network. In addition, weak C-HÁ Á ÁO hydrogen bonds are observed.
We gratefully acknowledge the financial support of the Education Office Foundation of Zhejiang Province (project No. Y201017321) and the innovation project of Zhejiang A & F University.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH5520). Carboxylic acids are important compounds, which have been widely used in various fields as coordination chemistry (Rueff et al., 2001), pharmaceutical chemistry (Strachan et al., 2007), and supramolecular chemistry (Desiraju, 2002).
Recently the main focus for carboxylic acids has been in crystal engineering via hydrogen bonded assembly of organic acids and organic bases (Grossel et al., 2006). As an extension of our study concentrating on hydrogen bonded assembly of organic acids and organic bases (Jin et al., 2012), herein we report the crystal structure of the title compound (I).

Figure 2
Part of the crystal structure with hydrogen bonds shown as dotted lines. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.  (7) 0.0050 (6) 0.0022 (7) Geometric parameters (Å, º)