2-{2-[4-(Dimethylamino)phenyl]diazen-1-ium-1-yl}pyridinium tetrachloridozincate

The title compound, (C13H16N4)[ZnCl4], consists of a tetrahedral [ZnCl4]2− anion and a 2-{2-[4-(dimethylamino)phenyl]diazen-1-ium-1-yl}pyridinium dication. The pyridinium-N atom is syn to the azo bond which allows for the formation of an intramolecular N—H⋯N hydrogen bond. In the crystal, the cation and anion are held together by N—H⋯Cl hydrogen-bond interactions involving the pyridinium and diazen-1-ium N atoms. π–π stacking interactions occur between the pyridine and benzene rings of adjacent cations [centroid–centroid distances = 3.6270 (18) and 3.8685 (18) Å]; the stacks are parallel to the a axis.

The mean value of the Zn-Cl bond distance of ZnCl 4 2anion is 2.266 (8) Å which is generally observed [2.268 (4) Å] (Harrison, 2005). The Cl-Zn-Cl bond angles in Fig. 1 2+ is doubly protonated on the pyridine N1 and azo N2 due to their higher electron density.
The N atom of the pyridine ring of the cation adopts a cis-orientation with respect to the azo moiety (-N2═ N3-) which is in contrast to the trans-geometry of the free dmazpy ligand (Leesakul et al., 2010). However, it is similar to an observation in a related crystal structure of 2-(4-hydroxyphenylazo)pyridine (3:1) tetrafluoroborate (Panneerselvam et al., 2000). Nevertheless, only single a protonation on the azo N3 was found. In the title compound, the dihedral angle of mean plane of pyridine-azo-phenyl rings is 2.38 (15)°. The N═N distance of the (H 2 dmazpy) 2+ is 1.313 (3) Å which is obviously longer than that of the free dmazpy ligand, 1.257 (16) Å. It may be caused by the protonation on the N atom of azo group which decreases the azo bond strength in comparison with the related free dmazpy ligand.

Refinement
The structure was solved by direct methods refined by a full-matrix least-squares procedure based on F 2 . All hydrogen atoms on C atoms were constrained, C-H = 0.9300 Å with U iso (H) = 1.2U eq (C) for C-sp 2 atoms and C-H = 0.9600 Å with U iso (H) = 1.5U eq (C) for C-sp 3 atoms of methyl groups, respectively. The hydrongen atoms of N atoms are located in a difference map and restrained, N-H = 0.89 Å with U iso (H) = 1.2U eq (N).

Figure 3
The π···π stacking between phenyl and pyriding rings of (H 2 dmazpy) 2+ . 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 > 2σ (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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq H2A 0.850 (5