The title compound [systematic name: 4-(2,2-diphenyl-2-prop­oxyacet­oxy)-1-methyl­piperidin-1-ium picrate], C23H30NO3 +·C6H2N3O7 −, crystallizes as a salt with one cation–anion (propiverinium picrate) pair in the asymmetric unit. A significant number of conformational changes are observed between the crystalline environment of this cation–anion salt and that of a density functional theory (DFT) calculation of the geometry-optimized structure. The angle between the dihedral planes of the two benzyl rings in the propiverinium cation increases by 14.4 (0)° from that of the crystalline environment. The dihedral angles between the mean planes of each of the benzyl rings and the mean plane of the piperidine increase by 2.0 (8) and 12.3 (5)°. The angles between the mean plane of the acetate group and the mean planes of the inter­connected piperidine group and the two benzyl rings decrease by 0.2 (1), 7.4 (6) and 3.2 (2)°, respectively. The mean plane of the phenolate group in the anion changes by +22.6 (9), +22.1 (1) and −2.8 (6)° from the mean planes of the piperidine and benzyl rings in the cation, respectively. In the crystal, a bifurcated N—H⋯(O,O) hydrogen bond and a weak C—H⋯π ring inter­action help to establish the packing. The two O atoms of the p-NO2 group are disordered with occupancies 0.825 (10):0.175 (10).

The crystal structure of chloranilic acid, C 6 H 2 Cl 2 O 4 , was first described by Andersen in 1967 [Andersen, E. K. (1967). Acta Cryst. 22, 188-191] at room temperature using visually estimated intensities. Taking into account the importance of the title compound, we have redetermined the structure at 100 (1) K. The approximately planar molecule [the maximum deviation from the mean plane through the ring is 0.0014 (9) Å for the ring atoms and 0.029 (3) Å for the other atoms] occupies a special position, lying across the center of symmetry. In the crystal structure, a two-dimensional hydrogen-bonded network sustained by O-HÁ Á ÁO interactions runs approximately parallel to [101]. The twodimensional layers are further packed in a parallel fashion, stabilized by ClÁ Á ÁCl interactions [ClÁ Á ÁCl = 3.2838 (8) Å , C-ClÁ Á ÁCl = 152.96 (6) ].

In the crystal structure of imatinibium dipicrate [systematic name: 1-methyl-4-(4-{4-methyl-3-[4-(3-pyrid­yl)pyrimidin-2-yl­amino]­anilinocarbon­yl}benz­yl)piperazine-1,4-diium dipicrate], C29H33N7O2+·2C6H2N3O7 −, the imatinibium cation is proton­ated at both of the pyrimidine N atoms. Each of the two picrate anions inter­acts with the diprotonated cation through bifurcated N—H⋯O hydrogen bonds forming R 1 2(6) ring motifs. Also, an R 2 2(24) graph set is formed between the benzamidium –NH– group and the 4-pyridyl N atom inter­acting through N—H⋯N hydrogen-bond inter­actions. Additional weak C—H⋯Cg π-ring and π–π inter­molecular inter­actions are observed which also influence crystal packing.

In the cation of the title compound [systematic name: (RS)-4-(3-carb­oxy-1-ethyl-6,8-difluoro-4-oxo-1,4-dihydro­quinolin-7-yl)-2-methyl­piperazin-1-ium 2,4,6-trinitro­phenolate], C17H20F2N3O3 +·C6H2N3O7 −, the piper­azine ring adopts a slightly distorted chair conformation and contains a protonated N atom. An intra­molecular O—H⋯O hydrogen bond occurs in the cation. The dihedral angles between the mean planes of the six-atom piperazine ring and the 10-atom fused ring system is 43.3 (5)°. The picrate anion inter­acts with the protonated N atom of an adjacent cation through a bifurcated N—H⋯(O,O) three-center hydrogen bond. Strong N—H⋯O hydrogen bonds in concert with weak π–π stacking inter­actions [centroid–centroid distance = 3.6460 (14) Å] dominate the crystal packing, creating a two-dimensional network structure along [011].

The title compound [systematic name: 3-(10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)-N,N,2-trimethyl­propan-1-aminium hydrogen maleate], C20H27N2 +·C4H3O4 −, a maleate salt of trimipramine, crystallizes with four independent cation–anion pairs in the asymmetric unit. The trimipramine cation contains a seven-membered azepine ring with two fused benzene rings whose mean planes are separated by 51.7 (1)°. Inter­molecular N—H⋯O and intra­molecular O—H⋯O hydrogen bonds pack the ions into chains along [101]. Additional weak inter­molecular C—H⋯O inter­actions help to influence the twist angles of the mean planes of the benzene rings fused to the azepine ring in the cation. A geometry-optimized MOPAC AM1 theoretical calculation supports these observations.