9-(4-Bromophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate

In the crystal structure of the title compound, C21H15BrNO2 +·CF3SO3 −, the cations form inversion dimers through π–π interactions between the acridine ring systems. These dimers are further linked by C—H⋯π and C—Br⋯π interactions. The cations and anions are connected by multidirectional C—H⋯O and C—F⋯π interactions. The acridine and benzene ring systems are oriented at 10.8 (1)°. The carboxyl group is twisted at an angle of 85.2 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel or almost parallel [inclined at an angle of 1.4 (1)°] in the crystal structure.

Cg1 and Cg2 are the centroids of the C9/N10/C11-C14 and C1-C4/C11/C12 rings, respectively. CgIÁ Á ÁCgJ is the distance between ring centroids. The dihedral angle is that between the planes of the rings I and J. CgI_Perp is the perpendicular distance of CgI from ring J. CgI_Offset is the distance between CgI and perpendicular projection of CgJ on ring I. 9-(4-Bromophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate D. Trzybinski, K. Krzyminski, A. Sikorski and J. Blazejowski

Comment
The cations of 9-(phenoxycarbonyl)-10-methylacridinium salts react efficiently with H 2 O 2 in alkaline media producing light (Zomer & Jacquemijns, 2001;Adamczyk & Mattingly, 2002). This effect means that the compounds can serve as chemiluminescent indicators or as chemiluminogenic fragments of chemiluminescent labels in assays of biologically and environmentally important entities such as antigens, antibodies, enzymes or DNA fragments (Zomer & Jacquemijns, 2001;Adamczyk & Mattingly, 2002;Roda et al. , 2003;King et al., 2007). The chemiluminogenic features of the compounds depend on the structure of the cations, particularly the phenoxycarbonyl fragment which is removed during their oxidation leading to electronically excited 10-methyl-9-acridinone molecules (Rak et al., 1999;Zomer & Jacquemijns, 2001). It has been found that the efficiency of chemiluminescence -crucial for analytical applications -is influenced by the constitution of the phenyl fragment (Zomer & Jacquemijns, 2001). This prompted us to synthesize and investigate derivatives substituted in this latter fragment. In this paper, a continuation of a series on bromo-substituted derivatives (Sikorski et al., 2005a), we present the structure of the title compound.
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., 2005a,b). With respective average deviations from planarity In the crystal structure, the inversely oriented cations form dimers through π-π interactions involving acridine moieties ( The C-H···O interactions are of the hydrogen bond type (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 π-π (Hunter et al., 2001) interactions. The C-Br···π interactions have been reported by others (Seo et al., 2009). The crystal structure is stabilized by a network of these short-range specific interactions and by long-range electrostatic interactions between ions.

Experimental
The title compound was obtained by treating 4-bromophenyl acridine-9-carboxylate [synthesized by heating acridine-9carboxylic acid with a tenfold molar excess of thionyl chloride and reacting the product thus obtained with an equimolar amount of 4-bromophenol (Sato, 1996;Sikorski et al., 2005b)] with a fivefold molar excess of methyl trifluoromethanesulfonate dissolved in dichloromethane (Sikorski et al., 2005a). The crude 9-(4-bromophenoxycarbonyl)-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 anhydrous ethanol (m.p. 504 -505 K).

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.
supplementary materials sup-8  (2) Symmetry code: (vi) -x, -y + 1, -z. Notes: Cg1 and Cg2 are the centroids of the C9/N10/C11-C14 and C1-C4/C11/C12 rings, respectively. CgI···CgJ is the distance between ring centroids. The dihedral angle is that between the planes of the rings I and J. CgI_Perp is the perpendicular distance of CgI from ring J. CgI_Offset is the distance between CgI and perpendicular projection of CgJ on ring I.