2,2′-[2,4-Bis(naphthalen-1-yl)cyclobutane-1,3-diyl]bis(1-methylpyridinium) bis(4-chlorobenzenesulfonate): thermal-induced [2 + 2] cycloaddition reaction of a heterostilbene

The asymmetric unit of the title salt, C36H32N2 2+·2C6H4ClO3S−, consists of one anion and one half-cation, the other half being generated by inversion symmetry. The dihedral angle between the pyridinium ring and the napthalene ring system in the asymmetric unit is 42.86 (6)°. In the crystal, cations and anions are linked by weak C—H⋯O interactions into chains along [010]. Adjacent chains are further arranged in an antiparallel manner into sheets parallel to the bc plane. π–π interactions are observed involving the cations, with centroid–centroid distances of 3.7664 (8) and 3.8553 (8) Å.

The asymmetric unit of the title salt, C 36 H 32 N 2 2+ Á-2C 6 H 4 ClO 3 S À , consists of one anion and one half-cation, the other half being generated by inversion symmetry. The dihedral angle between the pyridinium ring and the napthalene ring system in the asymmetric unit is 42.86 (6) . In the crystal, cations and anions are linked by weak C-HÁ Á ÁO interactions into chains along [010]. Adjacent chains are further arranged in an antiparallel manner into sheets parallel to the bc plane.interactions are observed involving the cations, with centroid-centroid distances of 3.7664 (8) and 3.8553 (8) Å .

Comment
Stilbene derivatives have been reported to exhibit non-linear optical (NLO) property (Ruanwas et al., 2010) and antibacterial activity (Chanawanno et al., 2010). It has been known that [2 + 2] photodimerization of stilbenes to yield cyclobutane can occur (Papaefstathiou et al., 2002). In our cases, the [2 + 2] cycloaddition of heterostilbene derivatives was carried out in solution by thermal-induced cycloaddition reaction, and we have previously reported the crystal structures of some of these derivatives (Chantrapromma et al., 2012;Fun, Surasit et al., 2009). The title compound (I) was obtained by the cycloaddition of trans-heterostilbene to give a syn headto-tail product (Yayli et al., 2004;Zhang et al., 2013). We report herein the synthesis and crystal structure of (I).

Experimental
A solution of (E)-1-methyl-2-[2-(1-naphthyl)vinyl)pyridinium iodide (0.25 g, 0.67 mmol) in CH 3 OH (20 ml) was mixed (1:1 molar ratio) with a solution of silver(I) 4-chlorobenzenesulfonate (0.20 g, 0.67 mmol) (Chantrapromma et al., 2007) in CH 3 OH (80 ml) and stirred for 30 min. The precipitate of silver iodide which formed was filtered and the filtrate was evaporated to give a yellow solid product. The yellow solid was repeatedly recrystallized for three times by dissolving the yellow solid in CH 3 OH and the solution was heated at 323 K to get a clear solution. The [2 + 2] cycloaddition of (E)-1methyl-2-[2-(1-naphthyl)vinyl)pyridinium occurred upon heating. Yellow plate-shaped single crystals of the title compound suitable for X-ray structure determination were obtained after recrystallization in CH 3 OH by slow evaporation of the solvent at room temperature after a few weeks.

Refinement
All H atoms were located in difference Fourier map and refined isotropically.

Figure 1
The molecular structure of the title compound, with 50% probability displacement ellipsoids. Symmetry code: (A) 2-x, 1y, 2-z,   The π···π stacking interactions between the pyridinium and napthalene rings. H atoms are omitted for clarity. are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.