catena-Poly[di-μ3-bromido-bis[(1-ethyl-1H-imidazole-κN 3)disilver(I)]]

The asymmetric unit of the title coordination complex, [Ag2Br2(C5H8N2)2]n, comprises a monodentate 1-ethylimidazole ligand, an Ag+ cation and a μ3-bridging Br− anion, giving a distorted tetrahedral AgNBr3 stereochemistry about the Ag+ cation [Ag—N = 2.247 (2) Å and Ag—Br = 2.7372 (4)–2.7523 (4) Å]. Two bridging bromide anions generate the dimeric [Ag2Br2(C5H8N)2] repeat unit [Ag⋯Ag = 3.0028 (5) Å], while a third Br− anion links the units through corner sharing in an inversion-related Ag2Br2 association [Ag⋯Ag = 3.0407 (4) Å], generating a one-dimensional ribbon step-polymer structure, extending along the c axis.


Related literature
For general background to N-heterocyclic carbenes, see: Arnold (2002); Lin & Vasam (2004). For related structures, see: Wang & Lin (1998); Liu et al. (2003); Helgesson & Jagner (1990, 1991; Chen & Liu (2003 Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.  Arnold (2002) and Lin & Vasam (2004). The products differ depending upon reaction conditions and the imidazolium salt used. Deprotonation by use of Ag 2 O has been the most widely used method in the syntheses of Nheterocyclic carbene complexes of silver. The procedure can be accomplished using the reaction of Ag 2 O with the imidazolium salt in CH 2 Cl 2 solution. The 3-diethylbenzole N-heterocyclic carbene complexes of silver have been successfully synthesized by the reaction of the 1,3-diethylbenzolium salt with Ag 2 O in CH 2 Cl 2 (Wang & Lin, 1998). In an attempt to prepare similar N-heterocyclic carbene complexes of silver by the reaction of Ag 2 O with 1,2-dibromocyclohexane and 1-ethylimidazole in DMSO solution, we obtained the title compound, [(C 5 H 8 N) 2 Ag 2 Br 2 ] n , instead and the synthesis and crystal structure are reported herein. Although the stair polymers of [(C 5 H 5 N) 4 Ag 4 I 4 ] n  and 1-allyl-3-methylimidazole carbine silver iodide (Chen & Liu, 2003) have recently been reported, their structural features are different from that of the title complex being formed through triple and quadruple halide bridges with Ag···Ag interactions.
Experimental 1,2-Dibromocyclohexane (2.42 g, 10 mmol) was added to a solution of 1-ethylimidazole (1.92 g, 20 mmol) in DMSO (100 ml) at room temperature and stirred for 2 h, after which Ag 2 O (2.32 g, 10 mmol) was added and the mixture was refluxed for 3 h with stirring. The volume of the solution was reduced to 50 ml under vacuum, the residue was removed by filtration and the filtrate was kept at room temperature for a few days. Colorless crystals of the title compound were

Refinement
The H atoms attached to C atoms of the imidazole ring were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). Methylene and methyl H atoms were likewise positioned geometrically (C-H = 0.99 and 0.98 Å, respectively) and also refined as riding atoms, and U iso (H) = 1.2U eq (C)

Figure 2
The step-polymeric structure of the title complex, extending along the c axial direction.

catena-Poly[di-µ 3 -bromido-bis[(1-ethyl-1H-imidazole-κN 3 )disilver(I)]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.68 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.