9-(Methylsulfanyl)acridinium trifluoromethanesulfonate

In the crystal structure of the title compound, C14H12NS+·CF3SO3 −, N—H⋯O hydrogen bonds link cations and anions into ion pairs. Inversely oriented ion pairs form stacks through multidirectional π–π interactions among the acridine units. The crystal structure features a network of C—H⋯O interactions among stacks and also long-range electrostatic interactions among ions. In the packing of the molecules, the acridine units are nearly parallel in stacks or inclined at an angle of 33.07 (2)° in the four adjacent stacks with which they interact via weak C—H⋯O interactions. The methylsulfanyl group is twisted through an angle of 60.53 (2)° with respect to the acridine ring.

In the crystal structure of the title compound, C 14 H 12 NS + Á-CF 3 SO 3 À , N-HÁ Á ÁO hydrogen bonds link cations and anions into ion pairs. Inversely oriented ion pairs form stacks through multidirectionalinteractions among the acridine units. The crystal structure features a network of C-HÁ Á ÁO interactions among stacks and also long-range electrostatic interactions among ions. In the packing of the molecules, the acridine units are nearly parallel in stacks or inclined at an angle of 33.07 (2) in the four adjacent stacks with which they interact via weak C-HÁ Á ÁO interactions. The methylsulfanyl group is twisted through an angle of 60.53 (2) with respect to the acridine ring.

Comment
Acridinium cations containing various substituents at position 9 and alkyl substitutes at the endocyclic N atom (position 10) are susceptible to oxidation by H 2 O 2 or other oxidants in alkaline media, leading to the formation of electronically excited 10-alkyl-9-acridinones capable of emitting light with a quantum yield of several percent (Zomer & Jacquemijns, 2001;Wróblewska et al., 2004). The chemiluminescence phenomenon described above is governed by the features of the substituent at position 9. In the search for derivatives that could exhibit enhanced chemiluminescence, we turned our attention to compounds in which the C atom at position 9 is bound to the S atom. The simplest compound that we were able to synthesize was 9-(methylthio)acridinium trifluoromethanesulfonate. It was obtained by the reaction of 9-thioacridinone (Berny et al., 1992) with methyl trifluoromethanesulfonate, which usually leads to quarternarization of the endocyclic N atom (Sato, 1996). The cation of the reaction product has a protonated endocyclic N atom, enabling it to react with oxidants, thereby facilitating the investigation of chemiluminescence phenomena. This paper presents the crystal structure of the title compound. This is, to our knowledge, only the second report on the crystal structure of an acridine derivatives S-substitued at position 9 (for the first one, see Mrozek et al., 2002).
In the crystal structure, N-H···O hydrogen bonds (Aakeröy et al., 1992) link cations and anions in ion pairs (Table 1,  are involved in multidirectional π-π interactions (Table 2, Fig. 2) of an attractive nature (Hunter et al., 2001). The crystal structure is stabilized by a network of C-H···O hydrogen type bonding interactions (Steiner, 1991;Bianchi et al., 2004) between neighbouring stacks (Figs 2 and 3) as well as by long-range electrostatic interactions between ions.
Experimental 9-(Methylthio)acridinium trifluoromethanesulfonate was synthesized in two steps. First, 9-thioacridinone was synthesized by heating with stirring a mixture of 9(10H)-acridinone, tetraphosphorus decasulfide and freshly distilled pyridine at 100°C for 1 h (Berny et al., 1992). The reactant mixture was subsequently poured into 30% aq ammonia and the resulting precipitate of 9-thioacridinone filtered off. This compound was then treated with a fivefold molar excess of methyl triluoromethanesulfonate dissolved in dichloromethane for 3 h (Ar athmosphere, room temperature) (Sato, 1996). The crude 9-(methylthio)acridinium trifluoromethanesulfonate thus formed was dissolved in a small amount of ethanol, filtered, and supplementary materials sup-2 again precipitated with a 25 v/v excess of diethyl ether (yield: 87%). Yellow crystals suitable for X-ray investigations were grown from absolute ethanol solution (m.p. 421-423 K).

Refinement
H atoms involved in C-H···O interactions were located in a difference map and refined without constrains. H atoms involved in N-H···O interaction were located in a difference map and refined using the N-H distance restraint of 0.86 (2) Å. Other H atoms were positioned geometrically, with C-H = 0.93 Å (aromatic) and 0.96 Å (methyl), and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) (aromatic) or U iso (H) = 1.5U eq (C) (methyl). Fig. 1. The molecular structure of the title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 25% probability level and H atoms are shown as small spheres of arbitrary radius. The N10-H10···O19 hydrogen bond is represented by a dashed line. Cg1, Cg2 and Cg3 denote the ring centroids.    (2) Symmetry codes: (ii) -x, -y+2, -z+1; (iii) -x+1, -y+2, -z+1. Notes: Cg1, Cg2 and Cg3 are the centroids of the C9/N10/C11-C14, C1-C4/C11/C12 and C5-C8/C13/C14 rings, respectively. Cg···Cg is the distance between ring centroids. The dihedral angle is that between the planes of the rings Cg I and Cg J . The interplanar distance is the perpendicular distance of Cg I from ring J. The offset is the perpendicular distance of ring I from ring J.