Bis[4-(dimethylamino)pyridinium] tetrachloridocuprate(II)

The asymmetric unit of the title salt, (C7H11N2)2[CuCl4], comprises half a tetrahedral tetrachloridocuprate anion, being located on a twofold axis, and a protonated 4-(dimethylamino)pyridine cation. The geometry around the CuII ion is highly distorted with the range of Cl—Cu—Cl angles being 94.94 (1)–141.03 (1)°. The crystal structure is stabilized by N—H⋯Cl and C—H⋯Cl hydrogen bonds. In the three-dimensional network, cations and anions pack in the lattice so as to generate chains of [CuCl4]2− anions separated by two orientations of cation layers, which are interlocked through π–π stacking contacts between pairs of pyridine rings, with centroid–centroid distances of 3.7874 (7) Å.

Electronic subshell d9 of Cu(II) is responsible for distortions of symmetry of the coordination polyhedron. This deals with the Jahn-Teller effect. The shape of the four-coordinated tetrahalocuprate (II) ions changes from square planar (Harlow et al., 1975) to distorted tetrahedral (Diaz et al., 1999) and the geometry of [CuX 4 ] 2species is influenced by the crystal-packing forces resulted from the size and the form of counter cations (Diaz et al., 1999;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 (Awwadi et al., 2007). The degree of distortion of [CuX 4 ] 2coordination polyhedra is determined by the mean value of the flattering or trans-angle θ. The asymmetric unit of the title compound, shown in figure 1, contains one half of the copper chloride salt, the other half is generated by a twofold rotation axis (4 e) on which Cu(II) is situated. The [CuCl 4 ] 2ions are highly distorted with a mean trans angle of 141.02° as a result of hydrogen bonding interactions with two nearly planar HDMAP cations (0.0295 Å mean deviation). The pyridinium nitrogen forms bifurcated hydrogen bond to two chloride ligands Cl1 and Cl2 and the created organic-inorganic hybrid compound (Fig. 2) is further assembled by C-H···Cl hydrogen bonding interactions (Table 2). In the three dimension network (Fig. 3), cations and anions pack in the lattice to generate chains of [CuX 4 ] 2anions separated by two orientations of cation layers which are interlocked through π-π stacking contacts between pairs of pyridine rings with distances centroid-centroid of 3.7874 (7) Å. All these interactions bonds link the layers together, forming a three-dimensional network and reinforcing the cohesion of ionic structure. Additionel hydrogen bond parameters are listed in table 1.
Evaporation of obtained solution at room temperature yields yellow crystals of the title compound after one week which crystals suitable for X-ray diffraction were carefully isolated.

Refinement
All H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent atoms (C and N) with C-H = 0.96 Å (methyl) or C-H = 0.93 Å (aromatic) N-H = 0.86 Å and with U iso (H) = 1.2 U eq (C aryl or N )and U iso (H) = 1.5 U eq (C methyl ).

Figure 1
A view of molecule structure of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.

Bis[4-(dimethylamino)pyridinium] tetrachloridocuprate(II)
Crystal data (C 7  Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.