title: Crystal structure of (4R,5S,6R)-6-azido-5-benz-yloxy-3,3,4-tri-fluoro-azepan-1-ium 2,2,2-tri-fluoro-acetate from synchrotron data.
abstract: 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 tri-fluoro-methane-sulfonate 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 mol-ecules. The two mol-ecules associate as a dimeric unit via two C-H⋯F inter-actions. 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.
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Alpesh Ramanlal
authors.initials: AR
authors.lastname: Patel
authors.affiliation: Mark Wainwright Analytical Centre, The University of New South Wales, Sydney, 2052 NSW, Australia.
authors.forename: Mohan M
authors.initials: MM
authors.lastname: Bhadbhade
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
keywords: azepane; crystal structure; fluorination; fluorine gauche effect; hydrogen bonding