Crystal structure of 9-aminoacridinium chloride N,N-dimethylformamide monosolvate

9-Aminoacridinium chloride N,N-dimethylformamide monosolvate was found to crystallize in the monoclinic space group P21/c. The crystal structure of this compound is stabilized by N—H⋯O and N—H⋯Cl hydrogen bonds, as well as π–π stacking.


Chemical context
Aminoacridine (AA) derivatives exhibit antibacterial (Ciric et al., 2011), anticancer (Hassan et al., 2011), antiviral (Kaur & Singh, 2011) and antiprion effects (Villa et al., 2011), as well as other therapeutic properties (Muregi & Ishih, 2010). The synthesis of these compounds and analysis of their interactions is very useful in view of their importance in a wide range of different biological systems (Coupar et al., 1997). Besides, numerous acridine-based derivatives are important for their chemiluminogenic ability and their use as chemiluminescent indicators in immunoassays, nucleic acid diagnostics and quantitative assays of biomolecules, such as antigens, antibodies, hormones and enzymes, as well as DNA-RNA structural analyses (Dodeigne, 2000;Becker et al., 1999). Additionally, photochemical reactions for these compounds in different media have been reported (Machulek et al., 2003). AA derivatives are promising analytical agents, since they exhibit relatively high quantum yields of light emission and stability (Adamczyk et al., 1999;Dodeigne, 2000;Renotte et al., 2000;Smith et al., 2009). 9-AA is a fluorescent dye of the family of nitrogen heterocyclic bases. 9-AA has been proposed as a specific fluorescent probe capable of binding the active center of guanidinobenzoatases (GB) (Murza et al., 2000). Interestingly, cellulose nanocomposites based on [Fe(hptrz) 3 ](OTs) 2 nanoparticles were effectively doped with 9-AA, resulting in a thermochromic and thermofluorescent material (Nagy et al., 2014). Previous crystallographic studies of some analogues of 9-AA have revealed that while in some members the acridine ring system is nearly planar (Carrell, 1972), in others it is ISSN 2056-9890

Supramolecular features
The packing of the molecules in the crystal is illustrated in Fig. 2. The crystal structure features N-HÁ Á ÁO and N-HÁ Á ÁCl hydrogen bonds (Table 1) as well asstacking interactions. The 9-AA molecules form layers (Fig. 3), which stack perpendicularly to the c axis. There are two types of 9-AA fused rings in the crystal structure, which results in the propagation of layers in a zigzag manner along b-axis direction (Fig. 2).

Figure 2
Crystal packing viewed along the c axis. The N-HÁ Á ÁCl and N-HÁ Á ÁO interactions are represented by green and red dashed lines, respectively. The A and B acridine molecules are coloured green and blue, respectively.

Figure 3
Layers of 9-AA.stacking interactions between the 9-aminoacridinium rings of different layers are shown by orange dashed lines.

Figure 1
The molecular structure of the title compound, showing the atomlabelling scheme and displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are represented by dashed lines. Two amine groups and two chloride ions form a supramolecular R 2 synthon (Etter, 1990;Etter et al., 1990;Aakerö y, 1997). The dimers are also stabilized by C-HÁ Á ÁCl hydrogen bonds between C atoms in positions 1 and 8 in the 9-AA skeleton and the halide ions [d(CÁ Á ÁCl) = 3.608 (5)-3.688 (4) Å and C-HÁ Á ÁCl = 163-172 ] (Fig. 2), as is also observed in other 9-AA salts (Sikorski & Trzybiń ski, 2011a,b;. Adjacent acridine skeletons are linked viastacking interactions in an AB arrangement (Fig. 3). All of the aromatic rings of the A molecules participate ininteractions, propagating in zigzag manner along the c-axis direction with centroid-centroid distances ranging from 3.9786 (3) to 4.2236 (3) Å . On the other hand, only the two aromatic rings of the acridine B molecules participate ininteractions, with adjacent acridine skeletons rotated in-plane with respect to one another. The centroid-centroid distances vary from 3.6514 (3) to 4.7445 (5) Å .

Database survey
A search of the Cambridge Structure Database (CSD version 5.42, last update February 2021; Groom et al., 2016) revealed that the current structure has never been published before. 101 structures containing 9-AA cations and chloride anions were found. These include 9-aminoacridine hydrochloride monohydrate (refcode: AMACRD; Talacki et al., 1974), which consists of a monoionized 9-aminoacride molecule with the proton on the N atom of the central ring, one water molecule, which is hydrogen bonded to another water molecule, and two chloride ions, which are hydrogen bonded to the amino group of the 9-AA cation. 9-Aminoacridinium 3-chlorobenzoate (AQAGEF; Sikorski & Trzybiń ski, 2011b) crystallizes in the monoclinic P2 1 /c space group with an 9-AA cation and a 3-chlorobenzoate anion in the asymmetric unit and the crystal structure features N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds andstacking interactions. Inversely oriented cations and anions form a tetramer; these ions are linked via N(amino)-HÁ Á ÁO (carboxy) hydrogen bonds, forming a ring motif. 9-Aminoacridinium 3-chlorobenzoate (AQAGIJ; (Sikorski & Trzybiń ski, 2011b) forms triclinic crystals (P1 space group) with an 9-AA cation, a 4-chlorobenzoate anion and a water molecule in the asymmetric unit. The crystal structure features N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds andinteractions. Analysis of the hydrogen bonds in the structure of this compounds shows that the ions form tetramers and produce an R 4 2 (16) hydrogen-bond ring motif. 9-Aminoacridinium 3hydroxybenzoate (AQAGOP; Sikorski & Trzybiń ski, 2011b) also crystallizes in the triclinic P1 space group, the asymmetric unit consisting of two 9-AA cations, 3-hydroxybenzoate and chlorate anions as well as two water molecules. This structure is the first of all the known 9-aminoacridinium salts where mixed salts were obtained (Allen, 2002). The average deviations from planarity of the acridine skeleton are 0.015 (2) and 0.027 (2) Å , and the angle between the mean planes of the right-and left-hand halves of the acridine skeleton is 1.5 and 3.7 in cations A and B, respectively. Analysis of the hydrogen bonds in this compound shows that the ions do not form tetramers, but produce two nearly perpendicularly aligned kinds of hydrogen-bonded chain motif. 9-Aminoacridinium chloride methanol solvate (SIDHAQ; Trzybiń ski & Sikorski, 2013) again forms triclinic crystals (P1 space group). The amino group of the 9-aminoacridinium cation interacts with the chloride anion via an N-HÁ Á ÁCl hydrogen bond and the methanol molecule via an N-HÁ Á ÁO hydrogen bond, generating a centrosymmetric R 4 2 (16) supramolecular synthon. The methanol molecule interacts with the halide ion; the resulting supramolecular synthon R 4 2 (12) is not planar but assumes a chair shape. This hydrogen-bonded ring motif is stabilized by the N-HÁ Á ÁCl hydrogen bond between the acridinium skeleton and the halide ion.

Synthesis and crystallization
9-Aminoacridinium hydrochloride (0.0624 g, 2.71Â10 À4 mol) was dissolved in N,N-dimethylformamide (4 ml) under heating at 418 K until the 9-AAÁHCl had fully dissolved. The solution was left to cool to 280 K. Single crystals were obtained after 2 days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed geometrically and refined as riding, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic hydrogens and the C-H group and C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for the CH 3 group. A rotating model was used for the methyl group.   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.