Bis(2-amino-6-methylpyridinium) tetrabromidocuprate(II)

In the crystal structure of the title compound, (C6H9N2)2[CuBr4], the geometry around the Cu atom is intermediate between tetrahedral (Td) and square planar (D4h). Each [CuBr4]2− anion is connected non-symmetrically to four surrounding cations through N—H⋯X (pyridine and amine proton) hydrogen bonds, forming chains of the ladder-type running parallel to the crystallographic b axis. These layers are further connected by means of offset face-to-face interactions (parallel to the a axis), giving a three-dimensional network. Cation π–π stacking [centroid separations of 3.69 (9) and 3.71 (1) Å] and Br⋯aryl interactions [3.72 (2) and 4.04 (6) Å] are present in the crystal structure. There are no intermolecular Br⋯Br interactions.

In the crystal structure of the title compound, (C 6 H 9 N 2 ) 2 [CuBr 4 ], the geometry around the Cu atom is intermediate between tetrahedral (T d ) and square planar (D 4h ). Each [CuBr 4 ] 2À anion is connected non-symmetrically to four surrounding cations through N-HÁ Á ÁX (pyridine and amine proton) hydrogen bonds, forming chains of the laddertype running parallel to the crystallographic b axis. These layers are further connected by means of offset face-to-face interactions (parallel to the a axis), giving a three-dimensional network. Cationstacking [centroid separations of 3.69 (9) and 3.71 (1) Å ] and BrÁ Á Áaryl interactions [3.72 (2) and 4.04 (6) Å ] are present in the crystal structure. There are no intermolecular BrÁ Á ÁBr interactions.
Al al-Bayt University and Al-Balqa'a Applied University are thanked for financial support.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2561).

S1. Comment
Non-covalent interactions play an important role in organizing structural units in both natural and artificial systems. They exercise important effects on the organization and properties of many materials in areas such as biology (Hunter 1994;Desiraju & Steiner 1999), crystal engineering (see for example: Allen et al.,1997;Dolling et al., 2001) and material science (Panunto et al., 1987;Robinson et al., 2000). The interactions governing the crystal organization are expected to affect the packing and then the specific properties of solids. In connection with ongoing studies (Ali & Al-Far, 2008;Ali & Al-Far, 2007;Al-Far & Ali, 2007a,b) of the structural aspects of halo-metal anion salts, we herein report the crystal structure of title compound (I) along with its crystal supramolecularity.
The asymmetric unit in (I) contains one anion and two cations (Fig. 1). The Cu-Br distances are similar, but Cu-Br2 that is engaged in longest hydrogen bonding is shorter than the others ( Table 2). The Cu-Br bond distances fall in the range of bond distances reported previously for compounds containing Cu-Br anions (Luque et al., 2001;Raithby et al., 2000;Haddad et al., 2006). The bond angles are present in two distinguished sets. The first contains four angles in the range 98.36 (6) -101.27 (6)° which are much lower than the other set which contains two angles 129.74 (7) and 132.23 (7)°. Accordingly the geometry of CuBr 4 2anion is an intermediate between regular tetrahedral (T d ) and square planar (D 4h ) ( Table 2).
The cation bond lengths and angles are within expected range (Allen et al. 1987), with the cations (type A contains N1 and type B contains N8) being of course planar.
In the structure (Fig. 2), each anion is connected nonsymmetrically to four cations interacting via N-H···Br and HN-H···Br hydrogen bonding, Table 3, forming chains of the ladder type run approximately parallel to the crystallographic baxis. The cations type A represnt the rungs while both cations type B and anions represent the rails of a ladder (Fig. 3).

S2. Experimental
To a warm solution of 2-amino-6-methylpyridine (2 mmol) dissolved in 10 ml absolute ethanol acidified with 3 ml 60% HBr, CuBr 2 (1 mmol) dissolved in 10 ml absolute ethanol was added. The resulting solution was then treated with 2 ml of Br 2 (l) . The mixture was refluxed for 2 h. The mixture was then allowed to stand and evaporate slowly at room temperature. In two days time, block blue crystals were formed and filtered (yield, 86.5%). A single-crystal suitable for diffraction measurements were chosen and used for data collection. and allowed to ride on their parent atoms with U iso fixed at 1.2 or 1.5 U eq (C,N).

Figure 1
A view of the asymmetric unit of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

bis(2-amino-6-methylpyridinium) tetrabromidocuprate(II)
Crystal data (C 6  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.57 e Å −3 Δρ min = −0.65 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.