2-{[2,8-Bis(tri-fluoro-meth-yl)quinolin-4-yl](hy-droxy)meth-yl}piperidin-1-ium tri-chloro-acetate: crystal structure and Hirshfeld surface analysis

The asymmetric unit of the centrosymmetric title salt, C17H17F6N2O+·C2Cl3O2 -, comprises a single ion-pair. The hy-droxy-O and ammonium-N atoms lie to the same side of the cation, a disposition maintained by a charge-assisted ammonium-N-H⋯O(hy-droxy) hydrogen bond [the Oh-Cm-Cm-Na (h = hy-droxy, m = methine, a = ammonium) torsion angle is 58.90 (19)°]. The piperidin-1-ium group is approximately perpendicular to the quinolinyl residue [Cq-Cm-Cm-Na (q = quinolin-yl) is -178.90 (15)°] so that the cation, to a first approximation, has the shape of the letter L. The most prominent feature of the supra-molecular association in the crystal is the formation of chains along the a-axis direction, being stabilized by charge-assisted hydrogen-bonds. Thus, ammonium-N+-H⋯O-(carboxyl-ate) hydrogen bonds are formed whereby two ammonium cations bridge a pair of carboxyl-ate-O atoms, leading to eight-membered {⋯O⋯HNH}2 synthons. The resulting four-ion aggregates are linked into the supra-molecular chain via charge-assisted hydroxyl-O-H⋯O-(carboxyl-ate) hydrogen bonds. The connections between the chains, leading to a three-dimensional architecture, are of the type C-X⋯π, for X = Cl and F. The analysis of the calculated Hirshfeld surface points to the importance of X⋯H contacts to the surface (X = F, 25.4% and X = Cl, 19.7%) along with a significant contribution from O⋯H hydrogen-bonds (10.2%). Conversely, H⋯H contacts, at 12.4%, make a relatively small contribution to the surface.