Crystal structure of 4-{2-[4-(dimethylamino)phenyl]diazen-1-yl}-1-methylpyridinium iodide

The molecular geometry of the ionic title compound, C14H17N4 +·I− or DAZOP+·I−, is essentially featureless. Regarding the crystal structure, in addition to the obvious cation–anion Coulombic interactions, the packing is mostly directed by non-covalent interactions involving both ring systems, as well as the iodide anion. It consists of cationic molecules aligned along [101] and disposed in an antiparallel fashion while linked into π-bonded dimeric entities by a stacking contact involving symmetry-related phenyl rings, with a centroid–centroid distance of 3.468 (3) Å and a slippage of 0.951 Å. The dimers are, in addition, sustained by a number of C—H⋯I and I⋯π (I⋯centroid = 3.876 Å) interactions involving the anion. Finally, interdimeric contacts are of the C—H⋯I and C—H⋯π types.

Cg2 is the centroid of the C12-C16/N17 ring.  (Gonbeau et al., 1999). This dye with donor-acceptor character, belongs to the group of the so-called non-linear optical chromophores (NLO-phore) that are able to form J-type aggregates (Coradin et al., 1997;Mestechkin, 2001;Nunzi et al., 2008). The crystal structures of this kind of NLO dyes are a topic of interest in this context and also for studies related to the solvatochromic properties of these dyes in hydrogen-bond-donor (HBD) and hydrogen-bond-acceptor (HBA) solvents. Very recently, new three-dimensional materials based on organic metalorganic frameworks (MOFs) with the capability to encapsulate dyes have been developed. All of these progress are aimed to the new photonic materials and devices design (Yu et al., 2013).

S2. Structural commentary
The title ionic compound [DAZOP + ][I − ] (I) crystallizes in the monoclinic S·G. P21/c, and presents one single molecule in the asymmetric unit. The molecular geometry, presented in Fig. 1, is essentially featureless.

S3. Supramolecular features
In addition to the obvious cation-anion coulombian interactions, the crystal packing is mostly directed by non covalent interactions involving the ring systems Cg1 (C4->C9) and Cg2 (C12->C16,N17, as well as the Iodine anion.
It consists of cationic molecules aligned along the [101] direction and disposed in an antiparallel fashion while linked into π bonded dimeric entities (

S4. Database survey
There are in the literature a lot of crystal structures derived from DAZOP but none with iodine as counter ion. The most similar to (I) is the one with CSD code (Allen, 2002) HANKUD (Cristian et al., 2004) which was solved using powder data and contains a molecule of hexafluorophosphate as counter ion. Thus although the molecules are practically the same, the differences between both structures are significant, mainly due to the absence of π-π interactions in HANKUD.

S5. Synthesis and crystallization
Benzenamine, N,N-dimethyl-4-(4-pyridinylazo)-was obtained as described in the literature (Li et al., 1995). It was then dissolved in acetonitrile and stirred while an excess of methyl iodide was added dropwise. The resultant mixture was refluxed for 3 h. After that, the orange precipitated obtained was further purified by column chromatography (1:4, methanol/ethyl acetate) with a yield of 59%. Single crystals were obtained by slow evaporation from a methanol solution using a Petri dish.

S6. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1 Figure 1 The molecular structure of (I),showing the atom-labelling scheme as well as the dimer formation. Displacement ellipsoids drawn at the 50% probability level. Symmetry codes: (i): 1 − x, 1 − y, 2 − z.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.00 e Å −3 Δρ min = −0.51 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.