Bis[4-(4-chlorophenyl)-4-hydroxypiperidinium] dipicrate dimethyl sulfoxide solvate

The asymmetric unit of the title salt solvate, 2C11H15ClNO+·2C6H2N3O7 −·C2H6OS, contains two crystallographically independent 4-(4-chlorophenyl)-4-hydroxypiperidinium cations, two picrate anions and a dimethyl sulfoxide solvent molecule. In each cation, the piperidinium ring adopts a chair conformation. In the crystal structure, the cations, anions and solvent molecules are connected by intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network.

During crystallization, the removal of the phenolic H atom leads to a shortening of the C12A-O2A = 1.246 (2) Å and C12B-O2B = 1.249 (2) Å bond lengths, indicating partial double bond character. This behaviour is similar to that observed in many picrate salts and is attributed to the loss of the hydroxyl proton at O2A and O2B, leading to the conversion of the neutral to an anionic state of the molecule. This leads to lengthening of the C12A-C13A = 1.454 (2) Å, C12A-C17A = 1.459 (3) Å (molecule A), C12B-C13B = 1.450 (3) Å and C12B-C17B = 1.454 (2) Å (molecule B) bonds compared to the remaining aromatic C-C distances in the picrate ions which has been observed in almost all picrate salts (Anitha et al., 2004;Thanigaimani et al., 2009).
The twist angles of the nitro groups of the each picrate anions shows that the ortho N2A and N4A nitro groups in molecule A and N2B and N4B groups in molecule B deviate from the benzene plane by 30.17 (11), 19.02 (11), 36.53 (11) and 19.73 (12) °, respectively.
supplementary materials sup-2 Experimental (4-Chlorophenyl)piperidin-4-ol (2.12 g, 0.01 mol) and and picric acid (2.4 g, 0.01 mol) were each dissolved in methanol (25 ml). The solutions were mixed and stirred in a beaker at 323 K for 30 minutes. The mixture was kept aside for three days at room temperature. The formed salt was filtered & dried in vacuum desiccator over phosphorous pentoxide (m.pt. 403-405 K). The salt was recrystallized from dimethylsulfoxide by slow evaporation to yield the title compound.

Refinement
All hydrogen atoms were positioned geometrically [O-H = 0.82 Å, N-H = 0.90 Å, and C-H = 0.93-0.97 Å] and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). In the absence of significant anomalous dispersion, 6635 Friedel pairs were merged for the final refinement.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.