Dimethylammonium guanidinium naphthalene-1,5-disulfonate

The asymmetric unit of the title salt, CH6N3 +·C2H8N+·C10H6O6S2 2−, consists of one dimethylammonium cation, one guanidinium cation, and two half naphthalene-1,5-disulfonate anions, which lie on inversion centers. N—H⋯O hydrogen bonds link the cations and anions into layers parallel to the ab plane. The layers have a sandwich-like structure, with the sulfonate groups and cations forming outer slices and the naphthalene ring systems inside.

The asymmetric unit of the title salt, CH 6 N 3 + ÁC 2 H 8 N + Á-C 10 H 6 O 6 S 2 2À , consists of one dimethylammonium cation, one guanidinium cation, and two half naphthalene-1,5disulfonate anions, which lie on inversion centers. N-HÁ Á ÁO hydrogen bonds link the cations and anions into layers parallel to the ab plane. The layers have a sandwich-like structure, with the sulfonate groups and cations forming outer slices and the naphthalene ring systems inside.

Comment
Recently a series of nanoporous materials has been reported, which have two-dimensional hydrogen-bond networks and adjustable porosity (Russell et al., 1997). Guanidinium ions and the sulfonate groups of arenedisulfonate ions can form rich variety of H-bonds. We prepared the title compound in attempts to find new hydrogen-bonded dielectric materials consisting of guanidinium and naphthalene-1,5-disulfonate ions. Unfortunately, the study of dielectric permeability of the title compound indicated that its dielectric constant is essentially temperature-independent below its melting point (388 -390 K). Thus we have found that the title compound has no dielectric disuniform from 80 K to 405 K.
At room temperature (25°C), the asymmetric unit of the title compound consists of one dimethylammonium cation, one guanidinium cation, and two halves of naphthalene-1,5-disulfonate anions, which lie at inversion centers ( Fig. 1). The N -H···O hydrogen bonds join cations and anions into layers parallel to the ab plane. Layers have sandwich-like structure: sulfonate groups and cations form outer slices and naphthalene bicycles are inside. (Fig. 2).

Experimental
The 1,5-naphthalenedisulfonic acid (1.824 g 8 mmol) and guanidinium tetrafluoroborate (0.588 g 4 mmol) were combined in 30 ml aqueous solution, and methanol solution of dimethylamine (0.326 g 4 mmol) was added to the mixture. The solution was stirred for 30 min to complete the reaction, and good quality blocky single crystals were obtained by slow evaporation of the filtrate after two weeks (chemical yield is 62%).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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.