catena-Poly[copper(II)-bis(μ-2-ethyl-5-methylimidazole-4-sulfonato-κ3 N 3,O 4:O 4′)]

In the title compound, [Cu(C6H9N2O3S)2]n, the copper(II) ion sits on an inversion center and is chelated by the imidazole N and sulfonate O atoms of two ligands in equatorial positions. O atoms of adjacent molecules coordinate in the axial positions. Jahn–Teller tetragonal distortion is evident in the coordination geometry [Cu—N and Cu—O equatorial distances of 1.971 (3) and 2.045 (2) Å, respectively, with a Cu—O axial distance of 2.433 (3) Å]. The structure is propagated by an infinite chain of eight-membered (Cu—O—S—O)2 ring systems along the a axis. Only N—H⋯O hydrogen bonding exists between the chains.

RJB wishes to acknowledge the NSF-MRI program (grant No. CHE-0619278) for funds to purchase the diffractometer, and we thank the Office of Naval Research for financial support.

Comment
In the title compound, the copper(II) ion sits on an inversion center and is chelated by the imidazole N1 and sulfonate O1 of two ligands. The two chelate rings on a Cu are 5-membered and co-planar. Two O3 O atoms of adjacent molecules coordinate the axial positions with the usual Jahn-Teller tetragonal distortion (Jahn & Teller, 1937)  Cu coordination is nearly octahedral, with adjacent angles ranging from 84.92 (10) to 93.10 (10)°. Our silver(I) complex of the same ligand (Purdy, et al. (2007)) has edge shared 8-membered rings connected by a tetrahedral Ag atom. The CuO 4 moieties are planar, and are nearly perpendicular (85.00 (8)°) to a plane composed of the linear N-Cu-N units within a chain. Likewise the plane formed by the 5-membered Cu-N-C-S-O chelate rings forms a dihedral angle of 86.61 (8)°w ith the plane formed by the Cu and O3 atoms within a chain.
The O2 atoms of the sulfonates are hydrogen bonded to the hydogen on N2 of the imidazole ring of an adjacent chain, at a N-O distance of 2.784 (4) Å. This interaction bonds the chains into a fully three-dimensional structure.

Experimental
Both 1:1 and 1:1.5 solutions of the potassium salts of the 2-ethyl-4-methyl-imidazole-5-sulfonic acid were prepared by combining 1 g (5.25 mmol) of the free acid with 1 and 1.5 equivalents of KOH solution respectively, and diluting the solutions to 1M based on K + . (All solutions were made with distilled water.) Two test reactions were done in vials with a 1M solution of CuCl 2 .2H 2 O, and a 0.2 ml metered pipet was used for the additions. In reaction #1, 0.2 ml of CuCl 2 solution was combined with 0.4 ml of the 1:1 solution. In reaction #2, 0.4 ml or the CuCl 2 solution was combined with 0.6 ml of the 1:1.5 solution. Both solutions were heated to a boil and allowed to cool. Both reactions produced a pale green precipitate, but green crystals of the title compound grow in #2 only, over several days. supplementary materials sup-2 Refinement H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with an N-H distance of 0.86 Å and C-H distances of 0.97 ÅU iso (H) = 1.2U eq (C) and 0.96 Å for CH 3 [U iso (H) = 1.5U eq (C)]. Fig. 1. Diagram of C 12 H 18 CuN 4 O 6 S 2 illustrating the atom numbering scheme used. Thermal displacement parameters are at the 30% probability level. [symmetry codes for labelled atoms: O1A, N1A, 1 -x, 1 -y, 1 -z; O3B, x -1, y, z; O3C, 2 -x, 1 -y, 1 -z]

catena-Poly[copper(II)-bis(µ-2-ethyl-5-methylimidazole-4-sulfonatoκ 3 N 3 ,O 4 :O 4' )]
Crystal data [Cu(C 6   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 Rfactors(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.

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