Supramolecular Incarceration and Extraction of Tetrafluoroberyllate from Water by Nanojars.

The previously unexplored noncovalent binding of the highly toxic tetrafluoroberyllate anion (BeF 4 2- ) 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 4 -binding propensity of [BeF 4 ⊂{Cu II (OH)(pz)} n ] 2- (pz = pyrazolate; n = 27-32) nanojars of different sizes is investigated using an array of techniques including mass spectrometry, paramagnetic 1 H, 9 Be, and 19 F NMR spectroscopy, and X-ray crystallography, along with thermal stability studies in solution and chemical stability studies toward acidity and Ba 2+ ions. The latter is found to be unable to precipitate the insoluble BaBeF 4 from nanojar solutions, indicating a very strong binding of the BeF 4 2- anion by nanojars. 9 Be and 19 F NMR spectroscopy allows for the unprecedented direct probing of the incarcerated anion in a nanojar and, along with 1 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 (Bu 4 N) 2 [BeF 4 ⊂{Cu(OH)(pz)} 32 ], which contains a novel Cu x -ring combination ( x = 9 + 14 + 9), (Bu 4 N) 2 [BeF 4 ⊂{Cu(OH)(pz)} 8+14+9 ], and (Bu 4 N) 2 [BeF 4 ⊂{Cu(OH)(pz)} 6+12+10 ] and offers detailed structural parameters related to the supramolecular binding of BeF 4 2- in these nanojars. The extraction of BeF 4 2- from water into organic solvents, including the highly hydrophobic solvent n -heptane, demonstrates that nanojars are efficient binding and extracting agents not only for oxoanions but also for fluoroanions.