Crystal structure of {bis[(1H-benzimidazol-2-yl-κN 3)methyl]sulfane}dichloridomercury(II)

In the asymmetric unit of the title compound, [HgCl2(C16H14N4S)], the HgII cation is linked to two Cl atoms and two imidazole N atoms of the chelating bis[(1H-benzimidazol-2-yl)methyl]sulfane ligand, forming a slightly distorted tetrahedral environment. The substitued imidazole rings of the ligand are almost perfectly planar [with maximum deviations of 0.017 (3) and 0.012 (3) Å] and form a dihedral angle of 42.51 (5)°. The crystal packing can be described as alternating layers parallel to (010). In this arrangement, N—H⋯Cl hydrogen bonds between the N—H groups of the benzimidazole moieties and chloride ligands are responsible for the formation of the chain-like packing pattern along [010] exhibiting a C(6) graph-set motif.

Data collection: APEX2 (Bruker, 2011); cell refinement: SAINT (Bruker, 2011); data reduction: SAINT; program(s) used to solve structure: SIR2002 (Burla et al., 2005); program(s) used to refine structure: SHELXT (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg & Berndt, 2001); software used to prepare material for publication: WinGX (Farrugia, 2012) and CRYSCAL (T. Roisnel, local program). Benzimidazole derivatives are reported to be physiologically and pharmacologically active (Tiwari, et al., 2007) and have shown different therapeutic properties such as antihypertensive, anticoagulant, antiallergic, analgesic, anti-inflammatory, antimicrobial, antiparasitic and antioxidant (Thimme Gowda, et al., 2009). Because of their significant medicinal importance, the synthesis of substituted benzimidazoles has become a focus of synthetic organic chemistry (Sondhi, et al., 2010). Benzimidazoles act as good ligands towards transition metal ions and give place to a variety of metal-ligand coordination modes. Their reactions with metal salts have played a significant role in the development of coordination chemistry of this class of ligands (Téllez, et al., 2008). Several research groups have investigated the coordination behavior of benzimidazole derivatives towards transition metal ions (Sundberg & Martin 1974;Reedijk, 1987) and numerous studies concerned with the biological activity of coordination compounds containing benzimidazole derivatives are also in progress.

S2. Structural commentary
Herein, we report the synthesis and structure determination of a new complex based on mercury and a chelating bisbenzimidazole ligand. The molecular structure of (I) together with the atomic numbering scheme is illustrated in Fig. 1

S3. Supramolecular features
The crystal packing can be described by alternating layers parallel to (010) (Figure 2). In this arragement N-H···Cl hydrogen bonds between amine moities and chloride ligands are responsible for the formation of the one-dimensional chain-like packing pattern exhibiting a C 1 1 (6) graph set motif (Etter et al., 1990;Bernstein et al., 1995). Additional hydrogen-bonding parameters are listed in Table 1. The packing is consolidated by π-π stacking interactions with centroid to centroid distances of 3.5525 (14) to 3.6963 (14) Å between benzimidazole rings. These interactions link the molecules within the layers and also link the layers together reinforcing the cohesion of the complex structure.

S5. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were localized on Fourier maps but introduced into calculated positions and treated as riding on their parent atom (C or N) with C-H = 0.93 Å (aromatic), C-H = 0.97 Å (methylene) and N-H = 0.86 Å (amine) with U iso (H) = 1.2U eq (C or N).

Figure 1
The molecular structure of the title compound with the atomic labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radii.

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.