Bis(trimethylammonium) naphthalene-1,5-disulfonate

The asymmetric unit of the title compound, 2C3H10N+·C10H6S2O6 2−, contains a half-anion, which is completed by inversion symmetry, and one cation. The cations and anions are associated via strong N—H⋯O(sulfonate) hydrogen-bonding interactions, forming cation–anion–cation groups. Secondary interactions such as C—H(ammonium)⋯O(sulfonate) and van der Waals interactions link the cations and anions together in a three-dimensional crystal structure, with zigzag rows of cations lying between layers of anions.

The asymmetric unit of the title compound, 2C 3 H 10 N + Á-C 10 H 6 S 2 O 6 2À , contains a half-anion, which is completed by inversion symmetry, and one cation. The cations and anions are associated via strong N-HÁ Á ÁO(sulfonate) hydrogenbonding interactions, forming cation-anion-cation groups. Secondary interactions such as C-H(ammonium)Á Á ÁO(sulf-O(sulfonate) and van der Waals interactions link the cations and anions together in a three-dimensional crystal structure, with zigzag rows of cations lying between layers of anions.
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: BH2404).

Structure Reports Online
Ferroelectric compounds have displayed a variety of technical applications, such as ferroelectric random access memories, infrared detectors, piezoelectric sensors, nonlinear optical devices, as a result of their excellent ferroelectric, piezoelectric, pyroelectric, and optical properties. Most of the new ferroelectric metal-organic compounds consistent with the necessary requirements for ferroelectric properties have been explored. However, the conditions required in these systems, such as a phase transition, a good electric hysteresis loop and electric domain, and a dielectric anomaly, often disappear (Zhang et al., 2009). Hence, pure organic compounds can be of great potential and can probably make up for the drawbacks found in ferroelectric metal-organic compounds. Reversible structural phase transition remains one of the prominent properties for ferroelectrics. For a small part of these compounds, the components can be arranged in a disordered fashion at a relative high temperature and in an ordered fashion at a relative low temperature. The transition from the disordered arrangement to the ordered one gives rise to sharp change in the physical properties of the compound (Fu et al., 2009;Zhang et al., 2008Zhang et al., , 2010Ye et al., 2006). As part of our search for simple ferroelectric compounds, we have investigated the title compound and report now its room temperature crystal 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, and thus forms a three-dimensional layered structure. The interactions tie the cations and anions together in sheets with zigzag rows of cations lying between layers of anions (Fig. 2). There are only van der Waals interactions between layers. The reported structure is similar to that of a related naphthalene-1,5-disulfonate salt (Wang & Yang, 2011).

Experimental
(C 3 H 10 N + ) 2 (C 10 H 6 S 2 O 6 2-) was formed from a mixture of N(CH 3 ) 3 (8 mL), C 10 H 8 O 6 S 2 (288.28 mg, 1.00 mmol), and distilled water (10 ml), which was stirred for few minutes at room temperature, giving a clear transparent solution. After evaporation over few days, block-shaped colorless crystals suitable for X-ray diffraction were obtained in about 82% yield, filtered and washed with distilled water.