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-⊂{<i>cis</i>-Cu^II(μ-OH)(μ-pz)}_<i>n</i>]^2- (<b>Cu</b>_{<b><i>n</i></b>}<b>XPO</b>_<b>3</b>; X = HO, H, F; <i>n</i> = 27-33; pz = pyrazolate) was explored. The nanojar hosts, which consist of stacks of three Cu_<i>x</i> (<i>x</i> = 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 (<b>Cu</b>_{<b>7+13+9</b>}<b>HPO</b>_<b>4</b>, <b>Cu</b>_{<b>8+13+8</b>}<b>HPO</b>_<b>4</b>, <b>Cu</b>_{<b>8+13+8</b>}<b>HPO</b>_<b>3</b>, and three pseudopolymorphs each for <b>Cu</b>_{<b>8+14+9</b>}<b>HPO</b>_<b>3</b> and <b>Cu</b>_{<b>8+14+9</b>}<b>FPO</b>_<b>3</b>) 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.