1,1′-(Butane-1,4-diyl)dipyridinium dibromide dihydrate

The organic cation in the title compound, C14H18N2 2+·2Br−·2H2O, is situated on an inversion centre. The cations, anions and water molecules are linked via O—H⋯Br, C—H⋯Br and C—H⋯O hydrogen bonds, and π–π stacking interactions between adjacent pyridine rings, with a centroid–centroid separation of 3.8518 (17) Å.


Structure Reports Online
Experimental A solution of 1,4-dibromine-butadinol (2.16 g, 0.01 mol) was added to a stirred solution of pyridine (1.98 g, 0.025 mol) in 1,4-dioxane (50 ml) at 110°C for 5 h. After cooling to room temperature, the mixture was filtered. The solid product was dissolved in 80 ml of water, and then set aside for three weeks to obtain colourless diamond-like crystals with average dimensions about 0.2 mm.

Refinement
All the H atoms were located in the difference Fourier map. The H atoms attached to the carbon atoms were situated into the idealized positions and refined in a riding-atom approximation. The constraints: C-H aryl =0.93 and C-H methylene =0.97 Å; U iso (H) = 1.2U eq (C).
The positional parameters of water H atoms were restrained with the distances O-H equal to 0.85 (1)Å while with the distance between both H atoms equal to 1.35 (2) Å. The water H atoms were refined as riding with U iso (H) = 1.2U eq (O). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code of C7 a : −x + 1, −y, −z + 1.

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 > 2sigma(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.