Bis[2,6-bis(2-methoxyphenyl)pyridinium] di-μ-bromido-bis[dibromidocuprate(II)]

The title salt, (C19H18NO2)2[Cu2Br6], was obtained from an attempt to synthesize the copper(II) complex of 2,6-bis(2-methoxyphenyl)pyridine (L) from a reaction between CuBr2 and one equivalent of L in CH2Cl2 at room temperature. The resulting compound is the salt of the 2,6-bis(2-methoxyphenyl)pyridinium cation and 0.5 equivalents of a hexabromidodicuprate(II) dianion. Both methoxy groups of the cationic pyridinium moiety are directed towards the N atom of the pyridine ring as a result of intramolecular N—H⋯O hydrogen bonds. The centrosymmetric hexabromidodicuprate dianion possesses a distorted tetrahedral geometry at the copper ion. The Cu—Br bond lengths are 2.3385 (7) and 2.3304 (7) Å for the terminal bromides, whereas the bond length between the Cu atom and two bridging bromides is slightly longer [2.4451 (6) Å].

Note that the centroid of the complete dianion coincides with the inversion center. Moreover, the hexabromodicuprate(II) dianion displays a distorted tetrahedral geometry at both copper(II) ions with Cu-Br bond distances of 2.3385 (7) and 2.3304 (7) Å for terminal bromides, and 2.4451 (6) Å for bridging bromides, respectively.
The neutral compound 2,6-bis(2-methoxyphenyl)pyridine has been previously reported (Silva et al., 1997) and their crystals were obtained from an ethyl acetate solution. The published crystal structure reveals that both methoxy groups are on opposite sides of the pyridine nitrogen to avoid the N···O lone pair repulsion. In addition, copper(II) complexes of the related ligand 2,6-bis(2'-hydroxyphenyl)pyridine have previously been synthesized and characterized (Steinhauser et al., 2004).

Experimental
The title compound, (C 9 H 18 NO 2 ).0.5(Cu 2 Br 6 ) (1), was prepared from a reaction of CuBr 2 (0.5 mmol) with one equivalent of 2,6-bis(2-methoxyphenyl)pyridine (0.5 mmol) in dichloromethane (30 ml) at room temperature for 3 h. The reaction solution was filtered to remove any unreacted CuBr 2 . X-ray quality single crystals were obtained from slow evaporation of a dichloromethane solution of 1 at room temperature.

Refinement
Structure refinement was performed using least-squares analysis. All non-H atoms were refined anisotropically whereas all H atoms were placed in calculated positions and treated as riding with C,N-H = 0.96 with U iso (H) = 1.2 U eq (C,N), including the methoxy H atoms.
Crystal data (C 19

Special details
Experimental. multi-scan from symmetry-related measurements SORTAV (Blessing 1995) Geometry. All standard uncertainties (except dihedral angles between l.s. planes) are estimated using the full covariance matrix. The   (6)