2-{[2,8-Bis(trifluoromethyl)quinolin-4-yl](hydroxy)methyl}piperidin-1-ium 3-amino-5-nitrobenzoate sesquihydrate

The asymmetric unit of the title salt solvate, C17H17F6N2O+·C7H5N2O4 −·1.5H2O, comprises a piperidin-1-ium cation, a 3-amino-5-nitrobenzoate anion, and three fractionally occupied [i.e. 0.414 (3), 0.627 (6) and 0.459 (5)] disordered water molecules of solvation. The cation has an L shape with a C—C—C—C torsion angle of −102.9 (3)° for the atoms linking the quinolinyl group to the rest of the cation. In the anion, the carboxylate and nitro groups are essentially coplanar with the benzene ring [O—C—C—C torsion angle = 179.7 (2)° and O—N—C—C torsion angle = −3.9 (3)°]. In the crystal, extensive O—H⋯O, O—H⋯F and N—H⋯·O hydrogen bonding leads to the formation of a layer in the ab plane.

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The confirmation of protonation at the amine-N2 atom is found in the nature of the intermolecular interactions, see below, as well as in the equivalence of the C-O bond distances [O2-C18 = 1.251 (4) Å and O3-C18 = 1.246 (4) Å] in the anion. Overall, the cation has an L-shaped conformation as the quinolinyl residue is approximately orthogonal to the rest of the cation; the C2-C3-C12-C13 torsion angle is -102.9 (3) °. The six-membered piperidin-1-ium ring adopts a chair conformation. The anion is effectively planar with both of the carboxylate [O2-C18-C19-C20 torsion angle = 179.7 (2)°] and nitro [O4-N3-C21-C20 torsion angle = -3.9 (3)°] groups being co-planar with the benzene ring to which it is connected The crystal packing is stabilized by hydrogen bonding, Table 1, that leads to layers in the ab plane. The carboxylate-O2 atom accepts two hydrogen bonds, one from the cation-OH and the other from the anion-amino-H. The carboxylate-O3 atom accepts a single interaction, i.e. from an ammonium-H. The second amino-H atom connects to nitro-O while the second ammonium-H hydrogen bonds water-O atoms. Water molecules form hydrogen bonds with each other and also donor hydrogen bonds to the cation-O atom, anion-O atoms and a weak contact to the F6 atom, Table 1. A view of the unit-cell contents is shown in Fig. 2 indicating layers stack along the c axis.

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.95-1.00 Å) and refined as riding with U iso (H) = 1.2U eq (C).
The O-H and N-H H atoms were located from a difference map and refined with O-H = 0.84±0.01 Å and N-H = 0.88-0.92±0.01 Å, respectively, and with U iso (H) = yU eq (O or N) with y = 1.5 for O and y = 1.2 for N. There are a total of 1.5 water molecules in the asymmetric unit and these are disordered over three positions with site occupancies factors of 0.414 (3), 0.627 (6) and 0.459 (5); hydrogen atoms were located for each of these and refined as described above. Fig. 1. The molecular structures of the components comprising the asymmetric unit in (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. The disordered water molecules of solvation have been omitted for reasons of clarity.

Special details
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.