9-Ethyl-10-methylacridinium trifluoromethanesulfonate

In the molecule of the title compound, C16H16N+·CF3SO3 −, the central ring adopts a flattened-boat conformation, and the two aromatic rings are oriented at a dihedral angle of 3.94 (2)°. In the crystal structure, weak intermolecular hydrogen bonds link the molecules. There are π–π contacts between the aromatic rings and the central ring and one of the aromatic rings [centroid–centroid distances = 3.874 (2), 3.945 (2) and 3.814 (2) Å]. There is also an S—O⋯π contact between the central ring and one of the O atoms of the anion.

In the molecule of the title compound, C 16 H 16 N + ÁCF 3 SO 3 À , the central ring adopts a flattened-boat conformation, and the two aromatic rings are oriented at a dihedral angle of 3.94 (2) . In the crystal structure, weak intermolecular hydrogen bonds link the molecules. There arecontacts between the aromatic rings and the central ring and one of the aromatic rings [centroid-centroid distances = 3.874 (2), 3.945 (2) and 3.814 (2) Å ]. There is also an S-OÁ Á Á contact between the central ring and one of the O atoms of the anion.
In the crystal structure, weak intermolecular hydrogen bonds (Table 1) link the molecules. The central ring B and the aromatic ring A are involved in multidirectional π-π interactions (Table 2, Fig. 2). One of the O atoms of the anion is involved in weak S-O···π interactions directed toward the center of the acridine ring system (Table 3, Fig. 2). The C-H···O (Bianchi et al., 2004;Steiner, 1999) interactions are of the hydrogen-bond type. The S-O···π interactions (Dorn et al., 2005) should be of an attractive nature, such as is also exhibited by π-π interactions (Hunter & Sanders, 1990). The crystal structure is stabilized by a network of the aforementioned short-range interactions, as well as by long-range electrostatic interactions between ions.
Experimental 9-Ethylacridine was synthesized by heating a mixture of N-phenylaniline with an equimolar amount of propanoic acid, both dispersed in molten zinc chloride (493 K, 26 h) (Tsuge et al., 1965). The crude product was purified by gravitational column chromatography (SiO 2 , n-hexane-ethyl acetate, 5:1 v/v). 9-Ethyl-10-methylacridinium trifluoromethanesulfonate was obtained by dissolving 9-ethylacridine with a fivefold molar excess of methyl trifluoromethanesulfonate in anhydrous dichloromethane and leaving the mixture for 3 h (Ar atmosphere, room temperature). The crude salt that precipitated was dissolved in a small amount of ethanol, filtered, and again precipitated with a 25 v/v excess of diethyl ether (yield; 89%).
Pale-yellow crystals suitable for X-ray analysis were grown from absolute ethanol solution.

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. 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.