Bis(2-trifluoromethyl-1H-benzimidazol-3-ium) tetrachloridomercurate dihydrate

In the title compound, (C8H6F3N2)2[HgCl4]·2H2O, the HgII cation is coordinated by four Cl− anions in a distorted tetrahedral geometry. In the crystal, the 2-trifluoromethyl-1H-benzimidazolium cations link to the [HgCl4]2− complex anions and lattice water molecules via N—H⋯Cl and N—H⋯O hydrogen bonds, and the lattice water molecules further link to the Hg complex anion and the organic cations via O—H⋯Cl and O—H⋯F hydrogen bonding. One of the trifluoromethyl groups is disordered over two orientations in a 0.59 (4):0.41 (4) ratio.

In the title compound, (C 8 H 6 F 3 N 2 ) 2 [HgCl 4 ]Á2H 2 O, the Hg II cation is coordinated by four Cl À anions in a distorted tetrahedral geometry. In the crystal, the 2-trifluoromethyl-1Hbenzimidazolium cations link to the [HgCl 4 ] 2À complex anions and lattice water molecules via N-HÁ Á ÁCl and N-HÁ Á ÁO hydrogen bonds, and the lattice water molecules further link to the Hg complex anion and the organic cations via O-HÁ Á ÁCl and O-HÁ Á ÁF hydrogen bonding. One of the trifluoromethyl groups is disordered over two orientations in a 0.59 (4):0.41 (4) ratio.

Ming-Liang Liu Comment
Recently much attention has been devoted to simple molecular-ionic compounds containing inorganic and organic ions due to the tunability of their special structural features and their potential ferroelectrics property. Ferroelectric materials that exhibit reversible electric polarization in response to an external electric field have found many applications such as nonvolatile memory storage, electronics and optics. The freezing of a certain functional group at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. (Fu et al, 2011;Ye et al. 2009;Zhang et al. 2009;Zhang et al. 2012;Zhang et al. 2010). In our laboratory, the title compound has been synthesized to investigate to its potentialferroelectric properties. However, it was found that the dielectric constant of the compound as a function of temperature indicates that the permittivity is basically temperatureindependent (ε = C/(T-T 0 )), suggesting that this compound is not ferroelectric or there may be no distinct phase transition occurring within the measured temperature (below the melting point).
The title compound,(C 8 H 6 F 3 N 2 ) 2 + .HgCl 4 2-.2H 2 O, has an asymmetric unit that consists of two 2-trifluoromethyl-1Hbenzimidazol cations, one tetrachloridomercuriate anion and two water molecules (Fig 1). The atoms of the benzimidazole ring are nearly coplanar and the triflouromethyl group lies out of this plane. The mercury cation is coordinated by six Clanions in distorted tetrahedral geometry.the average Hg-Cl bond distances range from 2.364 (2) Å to 2.564 (2) Å, the Cl-Hg-Cl angles range from 102.24 (8)°to 120.36 (9)°. In the crystal structure, the 2-trifluoromethyl-1H-benzimidazolecations are linked to adjacent tetrachloridomercuriate anions and watermolecules by N-H···O, N-H···Cl and O-H···Cl hydrogen bonds to form one dimensional chains parallel to ac plane (Fig 2). One of the trifluoromethyl is disordered.
Experimental 0.144 g (1 mmol) of 2-trifluoromethyl-1H-benzimidazol was firstly dissolved in 30 ml of ethanol which was added hydrochloric acid, to which 0.271 g (1 mmol) of mercuric chloride was added to give a solution at the ambient temperature. Single crystals suitable for X-ray structure analysis were obtained by the slow evaporation of the above solution after 5 days in air.   The packing of the title compound with view along the b axis. For the sake of clarity only the major component of the disordered trifluoromethyl group is shown.

Bis(2-trifluoromethyl-1H-benzimidazol-3-ium) tetrachloridomercurate dihydrate
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.022 Δρ max = 0.57 e Å −3 Δρ min = −1.28 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (