Bis(dicyclohexylammonium) sulfate dihydrate

In the title dihydrate salt, 2C12H24N+·SO4 2−·2H2O, the cation possesses twofold rotational symmetry, with the N atom situated on the twofold axis. The sulfate anion has fourfold roto-inversion symmetry, with the S atom located on the -4 axis. In the crystal, the components are linked via ammonium–sulfate N—H⋯O and water–sulfate O—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title dihydrate salt, 2C 12 H 24 N + ÁSO 4 2À Á2H 2 O, the cation possesses twofold rotational symmetry, with the N atom situated on the twofold axis. The sulfate anion has fourfold roto-inversion symmetry, with the S atom located on the 4 axis. In the crystal, the components are linked via ammoniumsulfate N-HÁ Á ÁO and water-sulfate O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Experimental
We are grateful to Professor H. Stoeckli-Evans, University of Neuchâ tel, for useful discussions while preparing this submission and to Professor Y. F. Diop

Comment
A number of sulfato complexes have been synthesized and characterized in order to study the behaviour of the sulfate anion as a ligand (Hathaway, 1973). The triammonium hydrogen disulfate salt has been prepared by the reaction of ammonia with sulfuric acid (Suzuki & Makita, 1978). In our laboratory, previous work on the behaviour of the sulfate ion has been studied especially in relation to tin(IV) complexes (Diassé-Sarr et al., 1997;Diallo et al., 2010;Diop et al., 2012). In the present work, we prepared the title salt by the reaction of aminoiminomethanesulfonic acid and dicyclohexylamine, and we describe herein its crystal structure.
The molecular structure of the title salt is illustrated in Fig. 1. The dicyclohexylammonium cation possesses two-fold rotational symmetry, with atom N1 situated on the two-fold axis. The sulfate cation has fourfold rotary inversion symmetry with atom S1 located on the 4.
In the crystal, the various units are linked via N-H···O(sulfate) and O-H(water)···O(sulfate) hydrogen bonds forming a three-dimensional network (Table 1 and Fig. 2).

Experimental
The title compound was obtained by reacting aminoiminomethanesulfonic acid with dicyclohexylamine in a 1:1 molar ratio in water. The solution was heated for 2 h, stirred for ca 8 h and then filtered. The filtrate was allowed to evaporation in a drying cupboard at 333 K, and yielded colourless block-like crystals of the title salt suitable for an X-ray diffraction analysis.

Refinement
The NH 2 and water H atoms were located in a difference Fourier map. The NH 2 H atom (the N atom is located on a twofold axis) was freely refined while the water H atom (the O atom is located on the two-fold axis) was refined with U iso (H) = 1.5U eq (O). The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.95 Å with U iso (H) = 1.2U eq (C).

Figure 2
A view along the b axis of the crystal packing of the title salt. Hydrogen bonds are shown as dashed lines (see Table 1  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.16 e Å −3 Δρ min = −0.12 e Å −3 Absolute structure: Flack (1983); 514 Friedel pairs Absolute structure parameter: 0.04 (10) 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 > 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.