Bis(2-amino-4-methylpyridinium) tetrachloridocuprate(II)

The asymmetric unit of the title compound, (C6H9N2)2[CuCl4], consists of one cation and one half-anion, bisected by a twofold rotation axis through the metal center. The anion exhibits a geometry that is intermediate between a Td and D 4h arrangement about the Cu atom. The crystal structure contains chains of cations alternating with stacks of anions. The cationic groups interact via offset face-to-face π–π stacking, forming chains running along the c axis. The anion stacks are parallel to the cation chains, with no significant inter- nor intrastack Cl⋯Cl interactions. There are several anion–cation hydrogen-bonding interactions of the (N—H)pyridine⋯Cl and (N—H)amino⋯Cl types, connecting the chains of cations to the stacks of anions. Both the N—H⋯Cl and π–π stacking interactions [centroid–centroid distances 3.61 (8) and 3.92 (2) Å] contribute to the formation of a three-dimensional supramolecular architecture.


Comment
Hybrid organic-inorganic low dimensional magnetic lattices of the formula (cation) 2 [MX 4 ] are of special interest (Coffey et al., 2000;and references therein). A wide variety of these complexes are known. Some examples are those containing a protonated pyridine and 2-aminopyrimidine (Coffey et al., 2000). The magnetic exchange in these compounds is mediated by van der Waals contacts between the halide ions of the [MX 4 ] 2pseudo-tetrahedra and the contacts are determined by the crystal packing. In connection with ongoing studies Ali & Al-Far 2007) of the structural aspects of organic-inorganic hybrids, here we report the crystal structure of Cu(II)-chloride complex with 2-amino-4-methylpyridinium as the organic cation.
The asymmetric unit in I contains one half anion (bisected by a two fold axis through the metal) and one cation ( Fig.  1). The Cu-Cl distances and Cl-Cu-Cl, angles, Table 1, fall in the range reported previously for compounds containing Cu-Cl anions (Raithby et al., 2000). The CuCl 4 2anion geometry is an intermediate between regular tetrahedral (T d ) and square planar (D 4 h ); the geometry of CuX 4 2anions will always distort from T d due to the Jahn-Teller effect, and this generally results in a compressed tetrahedral geometry. The extent of this compression is determined principally by electrostatic interactions with the environment -in this case, the hydrogen bonding.
In the cation bond lengths and angles are in accordance with normal values (Allen et. al., 1987).
The crystal packing ( Fig. 2) show alternating stacks of anions and chains of cations. The anion stacks are parallel to the cation chains, with no significant inter-and intra-stack Cl···Cl interactions. The cations interact via offset face-to-face, π-π stacking interactions leading to chains along the crystallographic c axis (Fig. 3), with alternating rings centroids separation distances of 3.61 (8) and 3.92 (2) Å.
Both N-H···Cl and π-π stacking interactions cause to the formation of a three-dimensional supramolecular architecture.

Experimental
To a hot solution (100 °C) of 2-Amino-4-methylpyridine (1 mmol) in 5 ml of CH 3 CN acidified with 2 ml of 3 M HCl, CuCl 2 .2H 2 O (1 mmol) dissolved in 10 ml CH 3 CN was added. The resulting mixture was refluxed for 1.5 h. The solution supplementary materials sup-2 was then allowed to stand undisturbed at room temperature. After 24 h yellow parallelepiped crystals were formed (yield: 0.170 g; 80.2%).