3-Ammoniopyridinium tetrabromidomercurate(II) monohydrate

The asymmetric unit of the title compound, (C5H8N2)[HgBr4]·H2O, consists of one cation, one anion and one water molecule. The anion exhibits a distorted tetrahedral arrangement about the Hg atom. The crystal structure contains alternating sheets of cations (in the ac plane) and stacks of anions. Several strong hydrogen-bonding interactions (pyN—H⋯Br and C—H⋯Br; py is pyridine), along with O—H⋯Br interactions, connect the sheets of cations to the stacks of anions. Cation–cation π–π stacking is also present (C⋯C distances in the range 3.424–3.865 Å). The shortest Br⋯Br distance is 3.9527 (9) Å.

The asymmetric unit of the title compound, (C 5 H 8 N 2 )-[HgBr 4 ]ÁH 2 O, consists of one cation, one anion and one water molecule. The anion exhibits a distorted tetrahedral arrangement about the Hg atom. The crystal structure contains alternating sheets of cations (in the ac plane) and stacks of anions. Several strong hydrogen-bonding interactions (pyN-HÁ Á ÁBr and C-HÁ Á ÁBr; py is pyridine), along with O-HÁ Á ÁBr interactions, connect the sheets of cations to the stacks of anions. Cation-cationstacking is also present (CÁ Á ÁC distances in the range 3.424-3.865 Å ). The shortest BrÁ Á ÁBr distance is 3.9527 (9) Å .
Al al-Bayt University and Al-Balqa'a Applied University are thanked for support.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CS2074). In the title compound, Fig. 1, the asymmetric unit contains one cation and one anion along with one water molecules.

3-Ammoniopyridinium tetrabromidomercurate(II
The anion exhibits a distorted tetrahedral arrangement about Hg atom ( Table 1). The Hg-Br1 and Hg-Br4 [2.5875 (6) and 2.5818 (7) Å, respectively] bonds are almost invariant and significantly shorter than Hg-Br2 and Hg-Br3 [2.6309 (7) and 2.6216 (7) Å, respectively]. These lengths fall within the range of Hg-Br distances reported previously for compounds containing [HgBr 4 ] 2anions (Al-Far et al., 2006;. It is noteworthy that the longer Hg-Br2, Br3 bonds are involved in more interactions than the shorter ones (Table 2). In the cation, the bond lengths and angles are in accordance with normal values (Orpen et al., 1989). The cation is, of course, planar, in which N1 and N2 atoms are also coplanar.
The packing can be regarded as sheets of cations in the ac plane that are separated by stacks of anions.

Experimental
A warm solution of HgCl 2 (1.0 mmol) dissolved in ethanol (10 ml) and HBr (60%, 3 ml), was added dropwise to a stirred hot solution of 2-aminopyridine (1 mmol) dissolved in ethanol (10 ml). After refluxing for 2 h, the mixture was filtered off, and then allowed to stand undisturbed at room temperature. The salt crystallized over 3 days as pink crystals. Crystals were filtered off and one crystal suitable for diffraction measurements was used to collect data.
supplementary materials sup-2 Refinement H atoms attached to water O atoms were located in a difference map and refined with restraints (O-H distance of 0.89 Å).
Other H atoms were positioned geometrically, with N-H = 0.86 Å (for py NH), N-H = 0.89 Å (for ammonium NH) and C-H = 0.93 Å for aromatic H, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C,N). Fig. 1. A view of the asymmetric unit with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.