Abstract
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.
Highlights
The formation of the piperidin-1-ium cation is supported by the pattern of hydrogen bonding involving the ammonium-N—H H atoms
An intramolecular ammonium-N+—HÁ Á ÁO(hydroxy) hydrogen bond is formed ensuring the hydroxyl-O1 and ammonium-N2 atoms are orientated to the same side of the cation with the O1—C12— C13—N2 torsion angle of 58.90 (19) angle indicating a + synclinal relationship
The most prominent feature of the packing is the formation of centrosymmetric, eight-membered {Á Á ÁOÁ Á ÁHNH}2 synthons, which arise as a result of ammonium-N+—HÁ Á ÁOÀ(carboxylate) hydrogen bonds whereby two ammonium cations bridge, via both hydrogen atoms, a pair of carboxylate-O2 atoms
Summary
Kryptoracemic behaviour is an interesting but rare phenomenon whereby enantiomeric molecules crystallize in one of the 65 Sohncke space groups. Sohncke space groups lack an inversion centre, a rotatory inversion axis, a glide plane or a mirror plane, implying Z0 would usually be greater than 1 (unless the molecule lies on a rotation axis) and in which enantiomeric molecules, when present, are related by a noncrystallographic symmetry, e.g. a non-crystallographic centre of inversion. Reviews of this phenomenon have appeared for organic compounds (Fabian & Brock, 2010) and for coordination complexes (Bernal & Watkins, 2015). Symmetry codes: (i) Àx þ 1; Ày; Àz þ 1; (ii) x À 1; y; z; (iii) Àx þ 1; Ày þ 1; Àz þ 1; (iv) Àx; Ày; Àz þ 2
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