Supramolecular Incarceration and Extraction of Tetrafluoroberyllate from Water by Nanojars.

The previously unexplored noncovalent binding of the highly toxic tetrafluoroberyllate anion (BeF) and its extraction from water into organic solvents are presented. Nanojars resemble anion-binding proteins in that they also possess an inner anion binding pocket lined by a multitude of H-bond donors (OH groups), which wrap around the incarcerated anion and completely isolate it from the surrounding medium. The BeF-binding propensity of [BeF⊂{Cu(OH)(pz)}] (pz = pyrazolate; = 27-32) nanojars of different sizes is investigated using an array of techniques including mass spectrometry, paramagnetic H, Be, and F NMR spectroscopy, and X-ray crystallography, along with thermal stability studies in solution and chemical stability studies toward acidity and Ba ions. The latter is found to be unable to precipitate the insoluble BaBeF from nanojar solutions, indicating a very strong binding of the BeF anion by nanojars. Be and F NMR spectroscopy allows for the unprecedented direct probing of the incarcerated anion in a nanojar and, along with H NMR studies, reveals the fluxional structure of nanojars and their inner anion-binding pockets. Single-crystal X-ray diffraction provides the crystal and molecular structures of (BuN)[BeF⊂{Cu(OH)(pz)}], which contains a novel Cu-ring combination ( = 9 + 14 + 9), (BuN)[BeF⊂{Cu(OH)(pz)}], and (BuN)[BeF⊂{Cu(OH)(pz)}] and offers detailed structural parameters related to the supramolecular binding of BeF in these nanojars. The extraction of BeF from water into organic solvents, including the highly hydrophobic solvent -heptane, demonstrates that nanojars are efficient binding and extracting agents not only for oxoanions but also for fluoroanions.