Crystal structure of (4R,5S,6R)-6-azido-5-benzyloxy-3,3,4-trifluoroazepan-1-ium 2,2,2-trifluoroacetate from synchrotron data

The structure of the title compound, C₁₅H₁₆F₆N₄O₃, was determined using synchrotron radiation on an extremely small crystal (0.015 × 0.01 × 0.01 mm). Although the diffraction was weak, leading to high residuals and a poor data-to-parameter ratio, the data allowed ready solution and refinement to reveal the entire structure. The solid-state structure is in accordance with the absolute configuration assigned based on that of the known starting material. The compound comprises a highly substituted seven-membered N-heterocyclic cation and a trifluoromethanesulfonate counter-anion. The title compound crystallizes with two independent cations (A and B) and anions (C and D) in the asymmetric unit. Two geminal F atoms, a single F atom, a benzyl ether and an azide group are substituted on consecutive C atoms between the NH₂ and CH₂ units of the azepan-1-ium ring system. The seven-membered rings adopt different conformations with the principal differences occurring in the CF₂CHFCH₂ segments of the ring systems. The geminal F atoms on the quaternary C atom exhibit essentially identical bond angles [109 (2) and 106 (2)°] in the two independent molecules. The two molecules associate as a dimeric unit via two C - H⋯F interactions. An extensive series of N - H⋯O, N - H⋯F, C - H⋯O, C - H⋯N, C - H⋯F and C - H⋯π contacts generate a three-dimensional network with cations and anions linked into ABCD repeat columns along a.