Triprolidinium dichloranilate–chloranilic acid–methanol–water (2/1/2/2)

In the triprolidinium cation of the title compound {systematic name: 2-[1-(4-methylphenyl)-3-(pyrrolidin-1-ium-1-yl)prop-1-en-1-yl]pyridin-1-ium bis(2,5-dichloro-4-hydroxy-3,6-dioxocyclohexa-1,4-dien-1-olate)–2,5-dichloro-3,6-dihydroxycyclohexa-2,5-diene-1,4-dione–methanol–water (2/1/2/2)}, C19H24N2 2+·2C6HCl2O4 −·0.5C6H2Cl2O4·CH3OH·H2O, the N atoms on both the pyrrolidine and pyridine groups are protonated. The neutral chloranilic acid molecule is on an inversion symmetry element and its hydroxy H atoms are disordered over two positions with site-occupancy factors of 0.53 (6) and 0.47 (6). The methanol solvent molecule is disordered over two positions in a 0.836 (4):0.164 (4) ratio. In the crystal, N—H⋯O, O—H⋯O and C—H⋯O interactions link the components. The crystal structure also features π–π interactions between the benzene rings [centroid–centroid distances = 3.5674 (15), 3.5225 (15) and 3.6347 (15) Å].


Related literature
Chloranilic acid is a strong dibasic organic acid which exhibits electron-acceptor properties on one hand and acidic properties leading to formation of hydrogen bonds on the other hand. In the case of stronger bases the proton-transfer, hydrogen bonded ion pairs will be formed which is interesting from the point of view of electron transfer reactions in biological systems. Also, protonation of the donor from acidic acceptors are generally a route for the formation of ion pair adducts. The synthesis and spectroscopic studies of charge transfer complexes between chloranilic acid and some As shown in Fig. 1, in the triprolidinium cation of (I), the N atoms on the pyridinium and pyrrolidine groups are protonated. The pyrrolidine group has an envelope conformation [the puckering parameters (Cremer & Pople, 1975) are The crystal structure is stabilized by N-H···O, O-H···O and C-H···O interactions (Table 1, Fig. 2). Furthermore, the crystal structure is stabilized via π-π interactions between the benzene rings [Cg3···Cg5(x, y, z) = 3.5674 (15) Å, are the centroids of the C13-C18, C1A-C6A and C1B-C6B benzene rings, respectively].

Experimental
Triprolidine hydrochloride (3.148 g, 0.01 mol) in 10 ml of methanol was mixed with chloranilic acid (2.09 g, 0.01 mol) in 10 ml of methanol. The mixture was kept aside for three days at room temperature. The formed salt was filtered and dried in a vacuum desiccator over phosphorous pentoxide. The compound was recrystallized from methanol solution by slow supplementary materials sup-2 . E68, o1037-o1038 evaporation (m.p.: 448-450 K with charring).

Refinement
The atoms of the methanol solvent molecule are disordered over two positions with the site-occupancy factors of 0.836 (4) and 0.164 (4). The hydroxyl H atoms of the neutral chloranilate molecule lying on an inversion centre are disordered over two positions with the site-occupancy factors of 0.53 (6) and 0.47 (6). The water H atoms were located in a difference Fourier map and refined with U iso (H) = 1.5U eq (O) and using the DFIX restraints for the O-H bond of 0.82 Å and the H···H distance of 1.297 Å. All of the remaining H atoms were placed in their calculated positions and refined using the riding model with C-H lengths of 0.84 Å (OH), 0.88 Å (NH), 0.93 Å (NH), 0.95 Å (CH), 0.99 Å (CH 2 ) or 0.98 Å (CH 3 ). Their isotropic displacement parameters were set to 1.2 (NH, CH, CH 2 ) or 1.5 (OH, CH 3 ) times U eq of the parent atom.

Figure 1
Molecular structure of (I) with the atom labeling scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. Only the major component of the disorder is shown.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.