Bis(2,6-dimethylpyridinium) tetrabromidocobaltate(II)

In the crystal structure of the title compound, (C7H10N)2[CoBr4], the [CoBr4]2− anion is connected to two cations through N—H⋯Br and H2C—H⋯Br hydrogen bonds to form two-dimensional cation–anion–cation layers normal to the crystallographic b axis. Interactions of the π–π type are absent between cations in the stacks [centroid–centroid separation = 5.01 (5) Å]. Significant intermolecular Br–aryl interactions are present in the structure, especially an unusually short Br–ring centroid interaction of 3.78 (1) Å. The coordination geometry of the anion is approximately tetrahedral and a twofold rotation axis passes through the Co atom.

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Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2543).
Bis(2,6-dimethylpyridinium) tetrabromidocobaltate(II) B. F. Ali, R. H. Al-Far and S. F. Haddad Comment Noncovalent interactions play an important role in organizing structural units in both natural and artificial systems (Desiraju, 1997). 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, 2007;Al-Far & Ali, 2007a,b) of the structural aspects of halo-metal anion salts, we herein report the crystal structure of the title compound (I) along with its crystal supramolecularity.
The asymmetric unit in (I), contains half an anion and one cation (Fig. 1 Zhang et al., 2005). In the cation, the bond lengths and angles are within normal range (Allen et al., 1987).

Experimental
Boiling CoCl 2 (1.0 mmol), dissolved in absolute ethanol (10 ml) was added to a stirred absolute ethanol solution (10 ml) of 2,6-lutidine (1 mmol) and 48% HBr (3 ml). The mixture was then treated with liquid Br 2 (2 ml). After refluxing for ca 1 h, the mixture was filtered off and allowed to evaporate undisturbed at room temperature. The salt crystallized out over 1 d as blue crystals. and allowed to ride on their parent atoms with U iso fixed at 1.2 or 1.5 U eq (C,N). Fig. 1. A view of the asymmetric unit of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry operation: (A) −x + 1, y, −z + 1/ 2].  Bis(2,6-dimethylpyridinium) tetrabromidocobaltate(II)

Figures
Crystal data (C 7