Diammonium biphenyl-4,4′-disulfonate

In the title salt, 2NH4 +·C12H8O6S2 2−, the dianion has crystallographic inversion symmetry. A three-dimensional framework is formed from primary hydrogen-bonded sheet structures comprising ammonium N—H⋯Osulfonate interactions and is linked peripherally through the biphenyl residues of the anions. This open framework has 43 Å3 solvent-accessible voids.

In the title salt, 2NH 4 + ÁC 12 H 8 O 6 S 2 2À , the dianion has crystallographic inversion symmetry. A three-dimensional framework is formed from primary hydrogen-bonded sheet structures comprising ammonium N-HÁ Á ÁO sulfonate interactions and is linked peripherally through the biphenyl residues of the anions. This open framework has 43 Å 3 solvent-accessible voids.

Comment
The guanidinium salts of biphenyl-4,4'-disulfonic acid (BPDSH 2 ) form two-dimensional hydrogen-bonded open-framework structures in which the guanidinium cations form sheets connected by BPDS pillars. (Russell et al., 1997). These structures may accommodate various molecular guest species, commonly aromatic hydrocarbons, giving crystalline clathrates of the type (Gu + ) 2 BPDS 2− . nG (where G = the guest species) (Swift, Pivovar et al., 1998;Swift & Ward, 2000;Pivovar et al., 2001). Because it was considered that the ammonium salt of BPDSH 2 might also have an open framework structure, we prepared crystals of anhydrous (NH 4 + ) 2 C 12 H 8 O 6 S 2 2− (I) from an aqueous ammoniacal solution of the acid and the structure is reported here.
In (I), the planar anions have inversion symmetry coincident with crystallographic symmetry (Fig. 1). Each ammonium cation gives a total of five associations with sulfonate-O acceptors of the cation (Table 1) resulting in sheet structures which extend across the bc planes in the unit cell at a = 0. These sheets are linked across the a cell direction through the biphenyl residues of the BPDS anions, giving a three-dimensional framework structure (Fig. 2). There are 43 Å 3 solvent accessible voids within the structure.

Experimental
Compound (I) was prepared by the room temperature interaction in a 2:1 stoichiometric ratio of ammonia as an aqueous solution with biphenyl-4,4'-disulfonic acid. Colourless crystal plates (m. p. >573 K) were obtained from the partial room temperature evaporation of this solution.

Refinement
The ammonium hydrogen atoms were located by difference methods and their positional and isotropic displacement parameters were refined. The aromatic H atoms were included in the refinement in calculated positions (C-H = 0.95 Å) using a riding model approximation, with U iso (H) = 1.2U eq (C). Fig. 1. Molecular configuration and atom naming scheme for the BPDS anion in (I). Atoms of the inversion-related half of the compound are indicated by symmetry code (vi) (−x + 1, −y, −z + 1). The dashed lines represent the hydrogen bonds between the ammonium protons and the sulfonate-O acceptors.

Fig. 2. A perspective view of the three-dimensional hydrogen-bonded framework structure of (I) with ammonium N-H-O sulfonate sheets interlinked by the biphenyl residues of the BPDS anions.
Diammonium biphenyl-4,4'-disulfonate

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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 > 2sigma(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.