Supramolecular Entrapping and Extraction of Selenate, Molybdate and Tungstate Ions from Water by Nanojars

The supramolecular binding exclusively by H-bonds of SeO₄^2-, MoO₄^2- and WO₄^2- ions to form nanojars of the formula [EO₄^2-⊂{cis-Cu^II(μ-OH)(μ-pz)}]^2- (CuEO; E = Se, Mo, W; n = 28-34; pz = pyrazolate) was studied in solution by electrospray ionization mass spectrometry, variable temperature, paramagnetic ¹H NMR and UV-vis spectroscopy, and in the solid state by single-crystal X-ray crystallography. These large anions allow for the observation of a record nanojar size, CuEO (E = Mo, W). Six crystal structures are described of nanojars of varying sizes with either SeO₄^2-, MoO₄^2- or WO₄^2- entrapped ions, including the first example of a cocrystal of two different nanojars in crystallographically unique positions, CuMoO and CuMoO. The latter provides unprecedented structural information about the Cu₈+Cu₁₄+Cu₁₀ ring combination of a nanojar with an entrapped tetrahedral anion. Also, the first crystal structure of a supramolecular host-guest complex with an entrapped WO₄^2- ion, CuWO is reported in this work. The relative strength of binding of SeO₄^2-, MoO₄^2- and WO₄^2- ions by nanojars of different sizes was assessed by reactivity studies toward Ba²⁺ ions and NH₃. Thermal stability studies of the various CuEO nanojars were conducted in DMSO-d₆ solutions over a 22-150 °C range. Furthermore, liquid-liquid extraction of SeO₄^2-, MoO₄^2- and WO₄^2- ions from water into an organic solvent by nanojars was investigated.