Heptane-1,7-diaminium sulfate monohydrate

The crystal structure of the title compound, C7H20N2 2+·SO4 2−·H2O, is presented, with particular focus on the packing arrangement in the crystal structure and selected hydrogen-bonding interactions that the compound forms. The crystal structure exhibits parallel stacking of the diammonium dication in its packing arrangement, together with inorganic–organic layering that is typical of these n-alkyldiammonium salts. An intricate three-dimensional hydrogen-bonding network exists in the crystal structure where the hydrogen bonds link the cation and anion layers together through the sulfate anions and the water molecules.

The author acknowledges the National Research Foundation Thuthuka programme (GUN 66314) and the University of Johannesburg for funding for this study. The University of the Witwatersrand is thanked for the use of their facilities and the use of the diffractometer in the Jan Boeyens Structural Chemistry Laboratory.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ZK2015). Heptane-1,7-diaminium sulfate monohydrate C. Arderne

Comment
The crystal structure of the title compound (I) adds to our current ongoing studies of long-chained diammonium inorganic mineral acid salts. Colourless crystals of heptane-1,7-diammonium sulfate hydrate were obtained from an attempt to synthesize heptane-1,7-diammonium sulfate. This material forms part of our structural chemistry study of the inorganic mineral acid salts of the n-alkyldiamines. A search of the Cambridge Structural Database (Version 5.32, Allen, 2002) revealed that this compound had not previously been determined.
The asymmetric unit of compound (I) contains one diammonium dication, one sulfate anion and one water molecule with all atoms occupying general positions. The hydrocarbon chain is also fully extended from N1 to C7 but then distorts from planarity through N2. This is evident in the C5-C6-C7-N2 torsion angle (-70.49° (18)). The molecular structure of (I) is shown in Fig. 1. showing a distinct inorganic-organic layering effect that is a common feature of these long-chained diammonium salts. An extensive three-dimensional hydrogen-bonding network is formed.
A close-up view of selected hydrogen bonding interactions can be viewed in Fig. 3. The three-dimensional hydrogen bonding network is built and linked through hydrogen bonding interactions between the ammonium groups of the dication and the sulfate anions and water molecules. These extensive interactions are seen to contribute to the distortion from planarity of the ω-end of the diammonium cation. The hydrogen bond distances and angles for the title compound (I) can be found in Table 2.

Experimental
Compound (I) was prepared by adding heptane-1,7-diamine (0.50 g, 3.84 mmol) to 33% sulfuric acid (H 2 SO 4 , 2 ml, 25.29 mmol, Merck) in a sample vial. The mixture was then refluxed at 363 K for 2 h. The solution was cooled at 2 K h -1 to room temperature. Colourless crystals of heptane-1,7-diammonium sulfate hydrate were collected and a suitable single-crystal was selected for the X-ray diffraction study.