Supramolecular Binding and Extraction of Phosphate, Phosphite and Fluorophosphate Anions from Water by Nanojars

In this work, the supramolecular binding of HPO₄^2-, HPO₃^2- and FPO₃^2- ions by nanojars of the general formula [XPO₃^2-⊂{cis-Cu^II(μ-OH)(μ-pz)}_n]^2- (Cu_nXPO₃; X = HO, H, F; n = 27-33; pz = pyrazolate) was explored. The nanojar hosts, which consist of stacks of three Cu_x (x = 6-14, except 11) metallamacrocycles, were studied in solution by electrospray-ionization mass spectrometry, variable-temperature, paramagnetic ¹H NMR and UV-vis spectroscopy, whereas the entrapped anion was probed using ¹⁹F and ³¹P NMR spectroscopy. In the solid state, X-ray diffraction on nine different single-crystals offers valuable information about the structure of the host-guest complexes (Cu₇₊₁₃₊₉HPO₄, Cu₈₊₁₃₊₈HPO₄, Cu₈₊₁₃₊₈HPO₃, and three pseudopolymorphs each for Cu₈₊₁₄₊₉HPO₃ and Cu₈₊₁₄₊₉FPO₃) and details of the supramolecular binding of the different phosphorus anions. Multinuclear NMR studies reveal that the different XPO₃^2- ions induce dramatic changes in the magnetism of a given nanojar, despite a less striking difference observed in their respective crystal structure, pointing to significantly different solution structures. The formation of HPO₃^2- and HPO₄^2- nanojars by anion exchange from CO₃^2- was also studied, along with the effects of NH₃ and Ba²⁺ ions on nanojar composition and thermal stability in solution. Furthermore, the liquid-liquid extraction of the HPO₄^2-, HPO₃^2- and FPO₃^2- anions from water into an organic solvent was demonstrated using nanojars as extractants.