1-Methyl-2-[(E)-2-(2-thienyl)ethenyl]quinolinium iodide1

In the title compound, C16H14NS+·I−, the cation has an E configuration about the C=C double bond of the ethylene unit. The dihedral angle between the thiophene ring and the quinolinium ring system is 11.67 (11)°. A weak C—H⋯S intramolecular interaction involving the thiophene ring generates an S(5) ring motif. In the crystal structure, the iodide ion, located between the cations arranged in an antiparallel manner, forms weak C—H⋯I interactions. The crystal structure is further stabilized by a π–π interaction between the thiophene and pyridine rings; the centroid–centroid distance is 3.6818 (13) Å.

In the title compound, C 16 H 14 NS + ÁI À , the cation has an E configuration about the C C double bond of the ethylene unit. The dihedral angle between the thiophene ring and the quinolinium ring system is 11.67 (11) . A weak C-HÁ Á ÁS intramolecular interaction involving the thiophene ring generates an S(5) ring motif. In the crystal structure, the iodide ion, located between the cations arranged in an antiparallel manner, forms weak C-HÁ Á ÁI interactions. The crystal structure is further stabilized by ainteraction between the thiophene and pyridine rings; the centroidcentroid distance is 3.6818 (13) Å .

Comment
The design and synthesis of conjugated compounds to search for second-order nonlinear optic (NLO) materials have generated extensive interest. From previous reports, both molecular orbital calculations (Morley, 1991) and experimental studies (Drost et al., 1995) have revealed that the products of dipole moment and molecular hyperpolarizability (υβ) of thiophenecontaining conjugated moieties are superior to that of benzene analogues. Based on this reason we have previously studied the compound containing thiophene unit, namely, 1-methyl-4-[(E)-2-(2-thienyl)ethenyl]-pyridinium 4-chlorobenzenesulfonate (Chantrapromma et al., 2008). In this paper we have synthesized the title compound which was designed by the replacement of the cationic 3-hydroxy-4-methoxyphenyl ring that is present in a compound possessing second-harmonic-generation (SHG) properties, 2-[(E)-2-(3-hydroxy-4-methoxyphenyl)ethenyl]-1methylquinolinium, iodide monohydrate (Chantrapromma, Jindawong, Fun & Patil, 2007) by the thiophene unit. Herein we report the synthesis and crystal structure of the title compound.
In the crystal packing (Fig. 2), the Iion is in between each pair of the two antiparallel cations and is linked with the cations through weak C-H···I interactions. The crystal is stabilized by weak C-H···S and C-H···I interactions (Table   1). A π-π interaction was observed with the Cg 1 ···Cg 2 distance of 3.6818 (13) Å; Cg 1 i and Cg 2 i are the centroids of the S1/C12-C15 and N1/C1/C6-C9 rings, respectively [symmetry code: The perpendicular distances of Cg 2 onto the plane of the S1/C12-C15 ring and Cg 1 onto the plane of the N1/C1/C6-C9 ring are 3.200 and 3.500Å, respectively supplementary materials sup-2

Refinement
All H atoms were placed in calculated positions (C-H = 0.93-0.96 Å) and were refined as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). A rotating group model was used for the methyl group. The highest residual electron density peak is located at 0.75 Å from atom I1 and the deepest hole is located at 0.38 Å from atom S1.
Figures Fig. 1. The title compound showing 50% probability displacement ellipsoids and the atomnumbering scheme. The weak C-H···S intramolecular interaction was drawn as a dashed line.

Special details
Experimental. The low-temparture data was collected with the Oxford Cryosystem Cobra low-temperature attachment. 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 > σ(F 2 ) is used only for calculating Rfactors(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.