Bis(3-hydroxypropanaminium) naphthalene-1,5-disulfonate

In the title molecular salt, 2C3H10NO+·C10H6O6S2 2−, the cations and anions are associated via N—H⋯O and O—H⋯O hydrogen-bonding interactions, giving rise to a three-dimensional structure with zigzag rows of cations lying between rows of anions. The asymmetric unit contains one cation and one half-anion, which is related to the remainder of the molecule by an inversion center.

In the title molecular salt, 2C 3 H 10 NO + ÁC 10 H 6 O 6 S 2 2À , the cations and anions are associated via N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bonding interactions, giving rise to a threedimensional structure with zigzag rows of cations lying between rows of anions. The asymmetric unit contains one cation and one half-anion, which is related to the remainder of the molecule by an inversion center.
The author thanks the Ordered Matter Science Research Center, Southeast University, for its excellent experimental conditions and its generous financial support.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: EZ2272).

Comment
Ferroelectric compounds have displayed such technical applications as ferroelectric random access memories (FeRAM), ferroelectric field-effect transistors, infrared detectors, piezoelectric sensors, nonlinear optical devices due to their excellent ferroelectric, piezoelectric, pyroelectric, and optical properties. A large number of new ferroelectric metal-organic coordination compounds corresponding to the necessary requirements for ferroelectric properties have been found, yet other necessary conditions, such as a phase transition, a good electric hysteresis loop and electric domain, and a dielectric anomaly, are often missed (Zhang et al., 2009). Therefore pure organic compounds are of great potential and can make up for the drawbacks found in ferroelectric metal-organic coordination compounds. Reversible phase transitions remain one of the prominent properties for ferroelectrics. There exists a series of compounds in which the components can be arranged in a disordered fashion at a relatively high temperature and in an ordered fashion at a relatively low temperature and where the transition is reversible, which is called a reversible structual transition (Fu et al., 2009;Zhang et al., 2010;Zhang et al., 2008;Ye et al., 2006). The transition from the disordered arrangement to the ordered one leads to a sharp change in the physical properties of the compound. As part of our search for simple ferroelectric compounds I have investigated the title compound and report here its room temperature structure.
The centrosymmetric anion and one cation are shown in Fig. 1 with the hydrogen bonds listed in Table 1. The existence of numerous hydrogen-bonding interactions helps to make the substance more stable, so that it forms a three-dimensional layered structure. These interactions tie the cations and anions together in sheets with zigzag rows of cations lying between rows of anions (Fig. 2).

Experimental
(C 3 H 10 NO) 2. (C 10 H 6 O 6 S 2 ) was formed from a mixture of NH 2 (CH 2 ) 3 OH (150.2 mg, 2.00 mmol), C 10 H 8 O 6 S 2 (288.28 mg, 1.00 mmol), and distilled water (10 ml), which was stirred a few minutes at room temperature, giving a clear transparent solution. After evaporation for a few days, block colorless crystals suitable for X-ray diffraction were obtained in about 78% yield and filtered and washed with distilled water.  Fig. 1. Crystal structure of the title compound with labelling and displacement ellipsoids drawn at the 30% probability level.  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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.4862 (