Bis(2,4-dimethylpyridinium) tetrabromidomercurate(II)

The asymmetric unit of the title compound, (C7H10N)2[HgBr4], consists of one cation and one half-anion, bisected by a twofold rotation axis passing through the metal atom. The anion exhibits a distorted tetrahedral arrangement about the HgII atom. In the crystal, the cations and anions are linked by N—H⋯Br hydrogen-bonding interactions along [010]. Cation–cation π–π stacking and Br⋯Br intermolecular interactions are absent.

The asymmetric unit of the title compound, (C 7 H 10 N) 2 - [HgBr 4 ], consists of one cation and one half-anion, bisected by a twofold rotation axis passing through the metal atom. The anion exhibits a distorted tetrahedral arrangement about the Hg II atom. In the crystal, the cations and anions are linked by N-HÁ Á ÁBr hydrogen-bonding interactions along [010]. Cation-cationstacking and BrÁ Á ÁBr intermolecular interactions are absent.
In the title compound, Fig. 1, the asymmetric unit of the title compound, (C 7 H 10 N) 2 [HgBr 4 ], consists of one cation and one half-anion, bisected by a twofold rotation axis passing through the metal center. The anion exhibits a distorted tetrahedral arrangement about the Hg atom ( Table 1). The Hg-Br1 and the symmetry related one [2.5767 (11)Å] bonds are almost invariant and significantly shorter than Hg-Br2 and symmetry related one [2.6160 (11)Å]. These lengths fall within the range of Hg-Br distances reported previously for compounds containing [HgBr 4 ] 2anions (Gowda et al., 2009;Li et al. 2009). It is noteworthy that the longer Hg-Br2 and the symmetry related bonds are involved in more and shorter interactions than the shorter bonds (Table 1). In the cation, the bond lengths and angles are in accordance with normal values (Allen et al., 1987). In the crystal structure the cations and anions are linked by N-H···Br hydrogen bonding interactions, Fig.2
Colorless crystals of the title salt formed in two days, filtered off and one crystal suitable for diffraction measurements is used to collect data.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with N-H = 0.86 Å and C-H = 0.93 and 0.96 Å, for aryl and methyl H-atoms, respectively. The U iso (H) were allowed at 1.5U eq (C methyl) or 1.2U eq (N/C nonmethyl).

Bis(2,4-dimethylpyridinium) tetrabromidomercurate(II)
Crystal data (C 7   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.45 e Å −3 Δρ min = −1.54 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.