1-Methyl-2-[(E)-2-(2-thienyl)ethenyl]quinolinium 4-bromobenzenesulfonate

In the title compound, C16H14NS+·C6H4BrO3S−, the cation exists in an E configuration and is essentially planar, the dihedral angle between the quinolinium and thiophene rings being 3.45 (9)°. The anion is inclined to the cation with dihedral angles of 75.43 (8) and 72.03 (11)°, respectively between the benzene ring and the quinolinium and thiophene rings. In the crystal, the cations and anions are arranged individually into separate chains along the c axis. The cation chains are stacked in an antiparallel manner along the a axis by π⋯π interactions with centroid–centroid distances of 3.7257 (13) and 3.7262 (14) Å. Weak C—H⋯O and C—H⋯π interactions link the cations and anions into a three-dimensional network. Short Br⋯S [3.7224 (5) Å] and Br⋯O [3.4267 (16) Å] contacts are also observed.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 (Chantrapromma et al., 2009a, b;Fun et al., 2009). With the knowledge that the organic dipolar compounds with extended π systems and having terminal donor and acceptor groups are likely to exhibit large hyperpolarizability (β) (Raimundo et al., 2002), the title compound (I) was designed and synthesized in order to study its NLO properties. Unfortunately (I) crystallizes out in a centrosymmetric P2 1 /c space group which precluded the second-order nonlinear optical properties.
The asymmetric unit of the title compound ( Fig. 1) consists of the C 16 H 14 NS + cation and C 6 H 4 BrO 3 Sanion. The cation exists in the E configuration with respect to the C10═C11 double bond [1.348 (3) Å] and is essentially planar with the dihedral angle between the quinolinium and the thiophene rings being 3.45 (9)° and the torsion angles C9-C10-C11-C12 = -179.8 (2)°. The ten non-H atoms of quinolinium unit lie on the same plane with an r.m.s. deviation of 0.0184 (2) Å. The relative arrangement of cation and anion is shown by the angles between the mean plane of the 4-bromophenyl ring and those of the quinolinium and thiophene rings which are 75.43 (8)° and 72.03 (11)°, respectively. The bond lengths are normal (Allen et al., 1987) and are comparable with those in related structures (Chantrapromma et al., 2006;Ruanwas et al., 2008).
Experimental 2-(2-Thiophenestyryl)-1-methylquinolinium iodide (compound A) was synthesized by mixing a solution (1:1:1 molar ratio) of 1,2-dimethylquinolinium iodide (2.00 g, 7.0 mmol), 2-thiophenecarboxaldehyde (0.64 ml, 7.0 mmol) and piperidine (0.69 ml, 7.0 mmol) in hot methanol (40 ml). The resulting solution was refluxed for 5 h under nitrogen atmosphere. The resultant solid was filtered off and washed with diethyl ether. Silver(I)4-bromobenzenesulfonate (compound B) was synthesized according to our previously reported procedure. (Chantrapromma et al., 2006). The title compound was synthesized by mixing compound A (0.10 g, 0.26 mmol) in hot methanol (50 ml) and compound B (0.09 g, 0.26 mmol) in hot methanol (20 ml). The mixture immediately yielded a grey precipitate of silver iodide. After stirring the mixture for ca. 45 min, the precipitate was removed and the resulting solution was evaporated yielding a brown solid. Brown block-shaped single crystals of the title compound suitable for x-ray diffraction analysis were recrystallized from methanol solvent by slow evaporation at room temperature over a few weeks. (Mp. 538-539 K).
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.75 Å from Br1 and the deepest hole is located at 0.55 Å from S1. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.