10-Methyl-9-phenoxycarbonylacridinium trifluoromethanesulfonate monohydrate

In the crystal structure of the title compound, C21H16NO2 +·CF3SO3 −·H2O, the anions and the water molecules are linked by O—H⋯O interactions, while the cations form inversion dimers through π–π interactions between acridine ring systems. These dimers are linked by C—H⋯O and C—F⋯π interactions to adjacent anions, and by C—H⋯π interactions to neighboring cations. The water molecule links two H atoms of the cation by C—H⋯O interactions and two adjacent anions by O—H⋯O interactions. The acridine and benzene ring systems are oriented at 15.6 (1)°. The carboxyl group is twisted at an angle of 77.0 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine units are either parallel or inclined at an angle of 18.4 (1)°.

In the crystal structure of the title compound, C 21 H 16 NO 2 + Á-CF 3 SO 3 À ÁH 2 O, the anions and the water molecules are linked by O-HÁ Á ÁO interactions, while the cations form inversion dimers throughinteractions between acridine ring systems. These dimers are linked by C-HÁ Á ÁO and C-FÁ Á Á interactions to adjacent anions, and by C-HÁ Á Á interactions to neighboring cations. The water molecule links two H atoms of the cation by C-HÁ Á ÁO interactions and two adjacent anions by O-HÁ Á ÁO interactions. The acridine and benzene ring systems are oriented at 15.6 (1) . The carboxyl group is twisted at an angle of 77.0 (1) relative to the acridine skeleton. The mean planes of the adjacent acridine units are either parallel or inclined at an angle of 18.4 (1) .

Comment
The crystal structures of six 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulfonates can be found in the Cambridge Structural Database. All of them were determined in our laboratory and concern derivatives substituted in the phenyl fragment. For a long time we were unable to obtain crystals of the parent compound, i.e. unsubstituted 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulfonate, suitable for X-Ray investigations. Eventually we succeeded, and we present here the crystal structure of the monohydrate of this compound. The reason for our interest in this group of compounds is their chemiluminogenic properties, which means they can be used as chemiluminescent indicators or the chemiluminogenic fragments of chemiluminescent labels (Zomer & Jacquemijns, 2001). These compounds are rouitenely applied in assays of biologically and environmentally important entities such as antigens, antibodies, enzymes or DNA fragments (Roda et al., 2003;Brown et al., 2009). The cations of the above mentioned salts undergo oxidation with hydrogen peroxide in alkaline media; at the same time the phenoxycarbonyl fragment is removed and the remainder of the molecule is converted to electronically excited, light-emitting 10-methyl-9-acridinone (Rak et al., 1999). This forms the basis for analytical applications (Zomer & Jacquemijns, 2001).
In the cation of the title compound ( Fig. 1), the bond lengths and angles characterizing the geometry of the acridinium moiety are typical of acridine-based derivatives (Sikorski et al., 2007;Trzybiński et al., 2009). With respective average deviations from planarity of 0.0292 (3) Å and 0.0016 (3) Å, the acridine and benzene ring systems are oriented at 15.6 (1)°.
The carboxyl group is twisted at an angle of 77.0 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine moieties are parallel (at an angle of 0.0 (1)°) or inclined at an angle of 18.4 (1)° in the lattice.
In the crystal structure, the anions form hydrates with water molecules through O-H···O interactions, while the inversely oriented cations form dimers through π-π interactions involving acridine moieties (Tables 1 and 3 (Bianchi et al., 2004;Novoa et al., 2006). The C-H···π interactions should be of an attractive nature (Takahashi et al., 2001), like the C-F···π (Dorn et al., 2005) and the π-π (Hunter et al., 2001) interactions. The crystal structure is stabilized by a network of these short-range specific interactions and by long-range electrostatic interactions between ions.

Experimental
The compound was synthesized following a procedure described elsewhere (Trzybiński et al., 2009). 9-(Chlorocarbonyl)acridine was prepared by treating acridine-9-carboxylic acid with a tenfold molar excess of thionyl chloride. The compound obtained was esterified with phenol in anhydrous dichloromethane in the presence of N,N-diethylethanamine and a catalytic amount of N,N-dimethyl-4-pyridinamine (room temperature, 15h). The product -phenyl acridine-9-carboxylate -was purified chromatographically (SiO 2 , cyclohexane/ethyl acetate, 3/2 v/v) and quaternarized with a five-fold molar excess of methyl trifluoromethanesulfonate dissolved in anhydrous dichloromethane (under an Ar atmosphere at room temperature for 3h) (Sato, 1996). The crude 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulfonate was dissolved in a small amount of ethanol, filtered and precipitated with a 25 v/v excess of diethyl ether. Yellow crystals suitable for X-ray investigations were grown from ethanol/H 2 O, 4/1 v/v, solution (m.p. 263-265K).

Special details
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.