Fluoride: Solution- and Solid-State Structural Binding Probe

Solid-state and solution studies were performed to determine if F− is encapsulated by anion hosts in both media. X-ray crystal structure determinations were compared with both 1H and 19F solution NMR data. Three hosts were studied: (1) two polyamide hosts, one with isophthaloyl spacers and the other with pyridine spacers, and (2) a polythioamide host with pyridine spacers. Binding studies showed that the pyridine-containing amide cryptand shows the highest affinity (Ka > 105 in DMSO-d6), with the other hosts at least a factor of 10 lower. All of the cryptands appear to encapsulate F− in solution, where a deuterium-exchange reaction with DMSO-d6 can be monitored by 19F NMR. Four crystal structures are reported and compared: two for the pyridine-containing free base hosts and two for encapsulated F− complexes of the two amide-based cryptands.