2-Chlorobenzene-1,4-diaminium bis(dihydrogenphosphate)

The asymmetric unit of the title salt, C6H9ClN2 2+·2H2PO4 −, contains two dihydrogenphosphate anions and one 2-chlorobenzene-1,4-diaminium dication. The H2PO4 − anions are interconnected through strong O—H⋯O hydrogen bonds to form two-dimensional infinite layers parallel to (001). The organic entities are anchored to the inorganic layers through N—H⋯O hydrogen bonds, and through weak C—Cl⋯O halogen bonds [3.159 (2) Å, 140.48 (7)°]. No π–π stacking interactions between neighboring aromatic rings or C—H⋯π interactions towards them are observed. Minor disorder is observed for the Cl atom and one hydroxy group [minor-component occupancy = 3.29 (9)%].

The title organic-inorganic hybrid material, while made from achiral components, crystallizes in the chiral space group P2 1 2 1 2 1 . The crystal investigated is partially racemically twinned, with a twinning ratio of 0.89 (4) to 0.11 (4). Its structure consists of one 2-chlorobenzene-1,4-diaminium dication and two crystallographically distinct H 2 PO 4anions ( Fig. 1). The chlorine atom is disordered over two chemically equivalent positions with a small but noticable presence of the second moiety (refined value 3.29 (9)%). Associated with this disorder is disorder of one phosphate hydroxyl group of one of the H 2 P(2)O 4anions, O6. Where not mentioned otherwise, this disorder is ignored in the following more detailed discussion of the structure.
The HPO 4 2anions show two types of P-O distances depending on whether the oxygen atoms are hydrogen donors or acceptors. As expected, the P-OH distances, varying between 1.54 (3) and 1.581 (1) Å, are significantly longer than the other P-O distances ranging from 1.500 (1) to 1.516 (1) Å. This is in agreement with the literature data (Chtioui & Jouini, 2006;Kaabi et al., 2004). Figure 2 shows that the H 2 PO 4anions are interconnected through O-H···O hydrogen bonds to form a two dimensional layer spreading parallel to the (0 0 1) plane at z = 0, 1/2 and 1 (Fig. 3). The organic cations, assembled in layers parallel to the H 2 PO 4anions at z = 1/4 and 3/4, are anchored to the inorganic layers through N-H···O hydrogen bonds whose geometrical characteristics are given in Table 1. The projection of the whole arrangement along the c-axis (Fig. 3) shows the alternating cationic and anionic layers. The structure also features a weak C-Cl···O halogen bond between the chlorine atom and one of the H 2 PO 4phosphate ions, a type of interaction that has recently attracted high levels of interest due to the observation of such interactions between halogenated compounds and the phosphate moieties in DNA (see e.g. Metrangolo & Resnati, 2008). In the title compound the Cl···O distance between Cl1 and O3 i is 3.159 (2) Å, the C-Cl···O angle 140.48 (7)° (symmetry operator (i) -x + 3, y + 1/2, -z + 3/2), the equivalent values for the interaction of the minor occupied Cl atom Cl1B with O6B are 2.91 (5) Å and 130 (1)°. While the Cl···O distances are shorter than the sum of the van der Waals radii of chlorine and oxygen (ca 3.3 Å, Bondi, 1964), the angles observed are on the small side for C-Cl···O halogen bonds (160-180°, see e.g. Politzer et al., 2007;Metrangolo & Resnati, 2001), indicating that the interactions observed are quite weak and more likely a result of the stronger hydrogen bonding interactions rather than one of the major driving forces determining the outcome of the assembly of the structural components of the title compound. No π-π stacking interactions between neighboring aromatic supplementary materials sup-2 Acta Cryst. (2013). E69, o159-o160 rings or significant C-H···π interactions towards them are observed.

Experimental
Crystals of the title compound were prepared at room temperature by slow addition of a solution of orthophosphoric acid (6 mmol in 20 ml of water) to an alcoholic solution of 2-chlorobenzene-1,4-diamine (3 mmol in 20 ml of ethanol). The acid was added until the alcoholic solution became turbid. After filtration, the solution was allowed to slowly evaporate at room temperature over several days leading to formation of transparent prismatic crystals with suitable dimensions for single-crystal structural analysis (yield 58%). The crystals are stable for months under normal conditions of temperature and humidity.

Refinement
The chlorine atom is disordered over two chemically equivalent positions with a small but noticable presence of the second moiety (refined value 3.29 (9)%). Associated with this disorder is disorder of one of the phosphate hydroxyl groups, O6. The minor moiety chlorine and oxygen atoms were constrained to have the same ADPs as their major moiety counterparts. Due to the low prevalence of the minor moiety no disorder was modeled for the aromatic ring the Cl atom is bonded to, despite of the obviously unrealistic C-C-Cl angles for the minor Cl atom.
All non hydrogen atoms were refined anisotropically. All H atoms were located in difference density Fourier maps, but were then placed in calculated positions riding on their respective carrier atom with C-H distances of 0.95, N-H distances of 0.91 Å, and O-H distances of 0.84 Å. Ammonium and hydroxyl H atoms were allowed to rotate but not to tip to best fit the observed electron density distribution. The position of the hydrogen atom of the minor occupied hydroxyl group was refined with a damping factor (DAMP 2000 in SHELXTL (Sheldrick, 2008)). In the final refinement cycles after removal of the damping factor its position was set to ride on its carrier oxygen atom. U iso (H) values were constrained to be 1.2 U eq (C) of the parent atom for C bound H atoms, and 1.5 times U eq (N/O) for N and O bound H atoms.
The compound was refined as a racemic twin. The twin ratio refined to 0.89 (4) to 0.11 (4).