Synthesis and structure of an aryltellurenium(II) cation; [4-tert-butyl-2,6-bis(1-pentyl-1H-benzimidazol-2-yl-κN 3)phenyl-κC 1]tellurium(II) (1,4-dioxane)triiodidomercurate(II)

In the structure of an aryltellurenium(II) salt containing a [4-tert-butyl-2,6-bis(1-pentyl-1H-benzimidazol-2-yl)phenyl]tellurium(II) cation and a [HgI3(dioxane)]− anion, the cation and anion are linked by a C—H⋯I interaction.

In the title salt, (C 34 H 41 N 4 Te)[HgI 3 (C 4 H 8 O 2 )], the aryltellurenium [C 34 H 41 N 4 Te] + cations and [HgI 3 (dioxane)] À anions are linked by a short interaction between the Te atom and one of the I-atom donors of the anion, as well as through weak C-HÁ Á ÁI interactions. The geometry around the Te atom is T-shaped with the coordination comprising a C atom of the central aromatic ring and two N atom donors of the benzimidazolyl moiety. The Te-N bond lengths are almost equal [2.232 (3) and 2.244 (3) Å ], while the Te-C bond length is 2.071 (4) Å . The N-Te-N bond angle is 150.68 (11) . The Hg II atom of the anion is coordinated by iodide ions from three sides and the fourth coordination site is occupied by an O atom of the solvent molecule (dioxane). Thus, it attains a trigonal-pyrimidal geometry, with O-Hg-I angles ranging of 90.76 (8) and 96.76 (7) and I-Hg-I angles ranging from 112.41 (1) to 125.10 (1) . The cations and anions are involved in numerous weakstacking interactions involving both the central phenyl ring and two inversion-related benzimidazole moieties, which propagate in the a-axis direction. In addition, there are numerous C-HÁ Á ÁI interactions between the cations and anions, which link them into a complex three-dimensional array.

Structural commentary
The title complex [C 34 H 41 N 4 Te] + [HgI 3 (dioxane)] À is shown in Fig. 2. It crystallizes in P2 1 /c in the monoclinic crystal system. The asymmetric unit contains one tellurenium cationic unit stabilized by a [HgI 3 (dioxane)] À counter-anion. The coordination geometry around the Te atom is T-shaped whereby each Te atom is bonded with the central carbon atom of the aromatic ring and intramolecularly coordinated with the two N atoms. This coordination gives rise to an octacyclic framework formed by two condensed five-membered rings, which is stable under ambient conditions. The observed Te-C bond length is 2.071 (4) (Bondi, 1964). This implies strong intramolecular TeÁ Á ÁN interactions in the tellurenium cation.
In the anion, the mercury atom is coordinated by three iodide ions and one oxygen atom from the solvent molecule (1,4-dioxane), with Hg-I bond lengths of 2.6828 (4), 2.6912 (4) and 2.7321 (3) Å , which are in the range expected for an Hg-I covalent bond (the sum of the covalent radii of Hg and I is 2.71 Å ). The Hg-O bond length of 2.730 (3) Å is longer than the sum of their covalent radii (2.15 Å ), but shorter than the sum of their van der Waals radii (3.07 Å ). This value is in the range found for previous Hg-dioxane structures [2.64 (1) to 2.83 (1) Å ; Small, 1982;Frey & Monier, 1971;     Diagram showing the atom-labeling scheme for the title compound, [C 34 H 41 N 4 Te] + [HgI 3 (dioxane)] À . The TeÁ Á ÁI interaction is shown as a dashed line. Displacement ellipsoids are drawn at the 30% probability level. Crochet & Fromm, 2011]. The O-Hg-I bond angles are 90.76 (8) , 95.08 (7) and 96.76 (7) and the I-Hg-I bond angles range from 112.41 (1) to 125.10 (1) . The resulting geometry around the mercury atom is thus trigonal pyramidal with the Hg atom displaced by only 0.2018 (3) Å from the plane of the three I atoms, with the longer Hg-O bond at the apex of this pyramid.

Supramolecular features
The molecules are involved in numerous weakstacking interactions involving both the central phenyl ring and the two benzimidazole moieties (symmetry code Àx + 1, Ày + 1, Àz + 1), which propagate in the a-axis direction, as shown in Fig. 3. The shortest separation, however, is 3.4980 (19) Å between the centroid of one of the outer phenyl rings (C24-C29; symmetry code Àx + 2, Ày + 1, Àz + 1) and the centroid of the moiety made up of the central phenyl ring and one of the imidazole rings (Te1/N1/N3/C1/C2/C7/C13-C18). There is a short interaction between the Te atom and one of the iodine donors from the anion [Te1Á Á ÁI1 = 3.8859 (4) Å ]. In addition there are numerous C-HÁ Á ÁI interactions between the cations and anions (Table 1), which link them into a complex threedimensional array (Fig. 3).

Database survey
A survey of the Cambridge Structural Database (web CSD version 1.19 with updates June 2017; Groom et al., 2016) reveals that there is no structure report in the literature for a tellurenium cation with bis-benzimidazole moieties, although an NCN pincer-framework-based tellurenium cation has one hit (Beleaga et al., 2011). There are four reports in the literature of structures involving Hg coordinated to dioxane (BIYPAA, Small, 1982;HGBDOX, Frey & Monier, 1971; VALRUX and VALSAE, Crochet & Fromm, 2011), including one which also contains Hg-I bonds (VALSAE, Crochet & Fromm, 2011).

Synthesis and crystallization
The reaction scheme for the synthesis of the title compound is shown in Fig. 1. To a solution of 1 (0.2 g, 0.269 mmol) in 1,4-dioxane (60 ml) was added 0.102 g of TeI 2 were added. The reaction mixture was stirred for 24 h at room temperature in an inert atmosphere. The reaction mixture was filtered. The filtrate was evaporated and reduced to 5 mL. Colorless prismatic crystals were obtained from slow evaporation of a1,4dioxane solution of the compound at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were positioned geometrically, with C-H = ranging from 0.95 to 0.99 Å , and allowed to ride on their parent atoms with U iso (H) = xU eq (C), where x = 1.5 for methyl H atoms and 1.2 for all other C-bound H atoms.

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