Structure of 2,2′-(5-tert-butyl-1,3-phenylene)bis(1-pentyl-1H-benzimidazol-3-ium) tetrachloridomercurate(II)

The structure of a 2,2′-[5-(tert-butyl)-1,3-phenylene)bis(1-pentyl-1H-benzimidazol-3-ium) salt of the tetrachloridomercurate(II) anion is reported in which there is an N—H⋯Cl⋯H—N trifurcated hydrogen bond.

In the title salt, (C 34 H 44 N 4 ) [HgCl 4 ], the [C 34 H 44 N 4 ] 2+ cations and [HgCl 4 ] 2À anions are linked by N-HÁ Á ÁCl hydrogen bonds. One of the two n-pentyl side chains was refined as disordered over two sets of sites, with occupancies of 0.733 (18) and 0.267 (18). The geometry around the Hg II atom in the [HgCl 4 ] 2À anion is distorted tetrahedral, with bond angles ranging from 98.16 (3) (13) Å ] for the Cl atom involved in a trifurcated hydrogen bond as an acceptor, including two N-HÁ Á ÁClÁ Á ÁH-N interactions as well as one C-HÁ Á ÁCl interaction. There are several C-HÁ Á ÁCl interactions, with CÁ Á ÁCl distances ranging from 3.492 (3) to 3.796 (3) Å . These link the cations and anions into a zigzag chain along the c-axis direction. In addition, there are ClÁ Á ÁCl halogen bonds, as well asinteractions, with centroid-to-centroid distances of 3.4765 (18) Å , which link one of the two benzimidazole moieties into dimeric units.

Structural commentary
The title compound, 3, is a salt which contains [C 34 H 44 N 4 ] 2+ cations and [HgCl 4 ] 2À anions linked by N-HÁ Á ÁCl hydrogen bonds. The reaction scheme leading to this product is shown in Fig. 1 (13) Å ] for the Cl atom involved in a trifurcated bond as an acceptor including two N-HÁ Á ÁClÁ Á ÁH-N inter-actions as well as one C-HÁ Á ÁCl interaction (see Table 1), as shown in Fig. 2. Unlike a similar structure published recently containing a closely related ligand (Rani et al., 2017a), where the Hg atom is bonded to an N atom from the benzimidazole moiety, in this instance a salt has been obtained due to the different conditions of the reaction. The structure has been published of a salt containing the tetrachloridomercurate(II) anion (Herbst et al., 2013) and a closely related ligand with nhexyl rather than n-pentyl side chains, which was the result of an attempted transmetallate reaction between Hg and Au.
In the ligand, the dihedral angles between the benzimidazole moieties and central phenyl ring are 40.60 (9) and 38.08 (10) , while the angle between them is 36.04 (6) . One of the pentyl substituents was refined as disordered over two sets of sites, with occupancies of 0.733 (18)/0.267 (18). The two pentyl side chains have adopted different conformations (for the disordered side-chain only values for the major conformation will be included) and this is illustrated by their torsion angles. Diagram showing the atom labeling scheme, the trifurcated bond involving an N-HÁ Á ÁClÁ Á ÁH-N hydrogen bond, the C-HÁ Á ÁCl interactions and the disorder in one n-pentyl side chain. Atomic displacement parameters are at the 30% probability level.

Figure 1
Reaction scheme showing the expected and actual products of the reaction.

Database survey
A survey of the Cambridge Structural database (CSD Version 5.37) for salts containing both the benzimidazole moiety as well as the tetrachloridomercurate(II) anion gave eight hits, including a closely related ligand with n-hexyl rather than npentyl side chains (Herbst et al., 2013).

Synthesis and crystallization
The reaction scheme is shown in Fig. 1. To a solution of 1 (0.2 g, 0.269 mmol) in dry 1,4-dioxane was added SbCl 3 (0.061 g, 0.269 mmol) at room temperature. The reaction mixture was refluxed for 6 h under an inert atmosphere of N 2 and filtered through Whatman filter paper. When the solvent was evaporated, a white-colored precipitate was obtained and purified by washing with hexane. The compound was dried under vacuum. Colourless block-shaped single crystals were Diagram showing the C-HÁ Á ÁCl interactions, which link the cations and anions into a zigzag chain in the c-axis direction. The minor component of the pentyl disorder has been omitted for clarity. Atomic displacement parameters are at the 30% probability level.

2,2′-(5-tert-Butyl-1,3-phenylene)bis(1-pentyl-1H-benzimidazol-3-ium) tetrachloridomercurate(II)
Crystal data (C 34  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.

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