Tetra-μ3-iodido-tetrakis{[ethyl 2-(1H-benzimidazol-1-yl)acetate-κN 3]copper(I)}

The complex molecule of the tetranuclear cubane-type title compound, [Cu4I4(C11H12N2O2)4], has crystallographically imposed fourfold inversion symmetry. The CuI ions are coordinated in a distorted tetrahedral geometry by an N atom of a benzimidazole ring system and three μ3-iodide ions, forming a Cu4I4 core. In the crystal, complex molecules are connected into a three-dimensional network by C—H⋯O hydrogen bonds involving H and O atoms of adjacent ethoxycarbonyl groups.

The complex molecule of the tetranuclear cubane-type title compound, [Cu 4 I 4 (C 11 H 12 N 2 O 2 ) 4 ], has crystallographically imposed fourfold inversion symmetry. The Cu I ions are coordinated in a distorted tetrahedral geometry by an N atom of a benzimidazole ring system and three 3 -iodide ions, forming a Cu 4 I 4 core. In the crystal, complex molecules are connected into a three-dimensional network by C-HÁ Á ÁO hydrogen bonds involving H and O atoms of adjacent ethoxycarbonyl groups.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RZ2757). Benzimidazoyl-based ligands have wide applications in physiological and pharmacological fields, such as treatment of hypoglycemia, inhibitory activity for the lymphoma of Burkitt, antimicrobial activity and other effects (Ramla et al., 2007;Barreca et al., 2007;Cetinkaya et al., 1999). Similarly, some metal complexes of benzimidazoyl derivatives possess interesting activities such as anti-viral, anti-cancers and anti-fungal activities (Snyderwine et al., 1997;Skog & Solyakov,2002;Garner et al., 1999). In particular, copper complexes are often used as chemical models of copper proteins and copper enzymes (Sorrell, 1989). Up to now, a number of structures of copper complexes involving the benzimidazol group have been reported (Sun et al., 2011;Liu et al., 2011;Toth et al., 1987), but no crystal structure of copper(I) complex based on ethyl 2-(1H-benzimidazol-1-yl)acetate is available. In order to contribute to this research field, we report herein the crystal structure of the title tetranuclear cubane-type complex.
In the title complex ( Fig. 1), each copper(I) metal of the Cu 4 I 4 core is coordinated by three µ 3 -iodide ions and a nitrogen atom of a benzimidazole ring system in a distorted tetrahedral geometry. The deviation from the ideal geometry can be  (14) %A. In the crystal structure (Fig. 2), complex molecules are connected into a three-dimensional network by C-H···O hydrogen bonds (Table 1)

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H = 0.93 Å) and were included in the refinement in the riding model approximation. The U iso (H) were allowed at 1.2 U eq (C).

Figure 2
Packing diagram of the title compound viewed along the c axis.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.004 Δρ max = 0.35 e Å −3 Δρ min = −0.32 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.