Triprolidinium dipicrate

In the tripodinium cation of the title compound {systematic name: 2-[(E)-1-(4-methylphenyl)-3-(pyrrolidin-1-ium-1-yl)prop-1-enyl]pyridinium bis(2,4,6-trinitrophenolate)}, C19H24N2 +·2C6H2N3O7 −, the N atoms on both the pyrrolidine and pyridinium groups are protonated. The pyrrolidine group adopts a slightly distorted envelope configuration. Strong N—H⋯O cation–anion hydrogen bonds and weak intermolecular N—H⋯O interactions link the dication and two anions. In both picrate anions, the nitro groups display rotational disorder over two orientations in a 0.605 (6):0.395 (6) ratio. The crystal packing also features weak intermolecular π–π [centroid–centroid distance = 3.8036 (14) Å] and C—H⋯O interactions.

ASD thanks the University of Mysore for research facilities and HSY thanks R. L. Fine Chemicals, Bangalore, for a gift sample of triprolidine hydrochloride. JPJ acknowledges the NSF-MRI program (grant No. CHE1039027) for funds to purchase the X-ray diffractometer.

Comment
Triprolidine, is a histamine H1 antagonist that competes with histamine for the normal H1-receptor sites on effector cells of the gastrointestinal tract, blood vessels and respiratory tract. Triprolidine has anticholinergic properties and is used to combat the symptoms associated with allergies and is sometimes combined with other cold medications designed to provide general relief for flu-like symptoms (Salunga et al., 1996). The crystal structures of triprolidine hydrochloride (James & Williams, 1971), triprolidine hydrochloride monohydrate (James & Williams, 1974) and triprolidine tetrachlorocuprate (II) (Parvez & Sabir, 1997) have been reported. In view of the importance of the title compound, this paper reports the crystal structure of (I), C 19 H 24 N 2 + . C 12 H 4 N 6 O 14 -.

Experimental
Triprolidine hydrochloride (3.15 g, 0.01 mol) was dissolved in 10 ml of methanol and picric acid (2.29 g, 0.01 mol) was dissolved in 10 ml of methanol. Both the solutions were mixed and stirred in a beaker at 333 K for 30 minutes. The mixture was kept aside for three days at room temperature. The formed salt was filtered & dried in a vaccum desiccator over phosphorous pentoxide. The compound was recrystallized from dimethyl sulphoxide by slow evaporation (m.p: 466-468 K).

Refinement
The oxygen atoms of three nitro groups on picrate cations are disordered over two positions in a ratio of 0.605 (6):0.395 (6).
H1N and H2N were located by a Fourier map and refined isotropically. All of the remaining H atoms were placed in their calculated positions and then refined using the riding model with C-H lengths of 0.95 Å (CH), 0.99 Å (CH 2 ) or 0.98 Å (CH 3 ).
The isotropic displacement parameters for these atoms were set to 1.2 (CH, CH 2 ) or 1.5 (CH 3 ) times U eq of the parent atom.

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) 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.