Bis(3-methylpyridinium) tetrachloridocuprate(II)

The title compound, (C6H8N)2[CuCl4], is composed of two 3-methylpyridinium cation and one tetrachloridocuprate(II) anion. The geometry around the copper(II) ion is that of a distorted tetrahedron. In the crystal structure, the anions and cations are linked by three different N—H⋯Cl hydrogen bonds. In addition, the crystal structure exhibits aromatic π–π interactions between the pyridinium rings of two discrete units [centroid–centroid distance = 3.704 (2) Å].

This study was supported financially by the Research Fund of Chungnam National University in 2008.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LX2094).

Comment
The four-coordinated tetrahalocuprate (II) ions, [CuCl 4 ] 2possess a variety of geometries from square planar to near tetrahedral symmetry, and the geometry of tetrahalocuprate (II) species is influenced by the crystal-packing forces resulted from the size and shape of counter cations (Schneider et al., 2007;Parent et al., 2007), hydrogen bonding to cations (Haddad et al., 2006;Marzotto et al., 2001;Choi et al., 2002), and halide-halide interactions in solid . Herein, we report the crystal structure of the title compound, bis(3-methylpyridinium)tetrachloridocuprate(II) (Fig. 1).
The [CuCl 4 ] 2anion in the title compound is distorted to be approximately D 2d , somewhat distorted from tetrahedral as a result of hydrogen bonding interactions with two 3-methylpyridinium cations. The range of Cl-Cu-Cl angles is 99.28 (2)-137.32 (2)°, which is far away from tetrahedral geometry. The Cl1 atom of [CuCl 4 ] 2anion forms a three-center hydrogen bond with two protonated pyridinium N atoms ( Fig. 2 & Table 1). On the other hand, the Cl2 atom forms a common two-center hydrogen bond with nicotinium cations. As shown in Fig. 2, there are weak π-π interactions between pyridinium rings of two discrete units. The Cg1···Cg2 i distance is 3.704 (2) Å (Cg1 and Cg2 are the centroids of the C1-C5/N1 pyridinium ring and the C7-C11/N2 pyridinium ring, respectively; symmetry code as in Fig.2 & Table 1).
These bands are tentatively assigned to d x ( 2 A 1 ), respectively.

Refinement
The H1 and H8 atoms were located in a difference map and refined freely. Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 -0.96 Å, and with U iso (H) = 1.2U eq (C) for aromatic and 1.5U eq (C) for methyl H atoms.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.