A series of 9 homologous sulfate-incarcerating nanojars [SO⊂{Cu(OH)(pz)}] (Cu; n = 27-33; pz = pyrazolate), based on combinations of three [Cu(OH)(pz)] rings (x = 6-14, except 11)-namely, 6 + 12 + 9 (Cu), 6 + 12 + 10 (Cu), 8 + 13 + 8 (Cu), 7 + 13 + 9 (Cu), 8 + 14 + 8 (Cu), 7 + 14 + 9 (Cu), 8 + 14 + 9 (Cu), 8 + 14 + 10 (Cu), and 9 + 14 + 10 (Cu)-has been obtained and characterized by electrospray-ionization mass spectrometry (ESI-MS), variable-temperature H NMR spectroscopy, and thermogravimetry. The X-ray crystal structure of Cu (8 + 13 + 8) is described. Cu and Cu, which are the largest nanojars in this series, are observed for the first time. Despite extensive overlap at a given temperature, monitoring the temperature-dependent variation of paramagnetically shifted pyrazole and OH proton signals in 60 different H NMR spectra over a temperature range of 25-150 °C and a chemical shift range from 41 ppm to -59 ppm permits the assignment of individual protons in six different sulfate nanojars in a mixture. As opposed to ESI-MS, which only provides the size of nanojars,H NMR offers additional information about their detailed composition. Thus, nanojars such as Cu (8 + 13 + 8) and Cu (7 + 13 + 9) can easily be differentiated in solution. High-temperature solution studies unveil a significant difference in the thermal stability of nanojars of different sizes obtained under kinetic control at ambient temperature, and aid in predicting the structure of the Cu nanojar, as well as in explaining the absence of the Cu ring from the Cu-Cu series. Anion exchange studies using sulfate and carbonate reveal that, although each anion is thermodynamically preferred by a nanojar of a certain size, the exchange of an already incarcerated anion is hampered by a substantial kinetic barrier. The remarkably strong binding of anions by nanojars allows for the extraction of highly hydrophilic anions, such as sulfate and carbonate, from water into organic solvents, despite their very large hydration energies.

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A comprehensive reactivity study of nanojars toward 18 different acidic compounds with varying pK, including 12 different carboxylic acids (both aliphatic and aromatic mono- and dicarboxylic acids), p-toluenesulfonic acid, hydrogen sulfate, hydrogen carbonate, carbonic acid, 1-decanethiol, and methanol, as well as four different conjugate bases (formate, acetate, benzoate, 2-bromoethanesulfonate) is carried out with the aid of electrospray-ionization mass spectrometry. Thus, the effect on nanojar substitution and breakdown pattern of a number of variables, such as concentration of reagent (acid or conjugate base), acidity of reagent (pK), effect of acid vs conjugate base, steric effects, aromaticity, incarcerated anion and size of the nanojar, is evaluated. Of the substitution and breakdown products identified by mass spectrometry, acetate-substituted nanojars (BuN)[CO⊂{Cu(μ-OH)(μ-pz)(μ-CHCOO)}] (x = 1 and 2), as well as dimeric complexes (BuN)[Cu(μ-pz)A] (A = CO and SO) have been isolated and characterized by single-crystal X-ray diffraction. This study offers a detailed understanding of the behavior of nanojars of various sizes and with different incarcerated anions in the presence of the above-mentioned compounds at varying concentrations and tests the limits of the pyrazolate/carboxylate structural analogy in multinuclear metal complexes. The results point to the possibility of obtaining functionalized nanojars via pyrazolate/carboxylate ligand exchange, an aid in the design of anion extraction processes using nanojars or similar complexes as extracting agents.

The unprecedented liquid−liquid extraction of the dinegative chromate ion (CrO 4 2− ) from neutral aqueous solutions into aliphatic hydrocarbon solvents using nanojars as extraction agents is demonstrated. Transferring chromate from water into an organic solvent is extremely challenging due to its large hydration energy (ΔG h °= −950 kJ/mol) and strong oxidizing ability. Owing to their highly hydrophilic anion binding pockets lined by a multitude of hydrogen bond donor OH groups, neutral nanojars of the formula [cis-Cu II (μ-OH)(μ-4-Rpz)] n (n = 27−33; pz = pyrazolate anion; R = H or n-octyl) strongly bind the CrO 4 2− ion and efficiently transfer it from water into n-heptane or C 11 − C 13 isoalkanes (when R = n-octyl). The extracted chromate can easily be recovered from the organic layer by stripping with an aqueous acid solution. Electrospray ionization mass spectrometric, UV−vis and paramagnetic 1 H NMR spectroscopic, X-ray crystallographic, and thermal stability studies in solution and chemical stability studies toward NH 3 , methanol, and Ba 2+ ions are employed to explore the binding of the CrO 4 2− ion by nanojars. Titration of carbonate nanojars [CO 3 ⊂ {Cu(OH)(pz)} n ] 2− with H 2 CrO 4 leads to anion exchange and the formation of chromate nanojars [CrO 4 ⊂ {Cu(OH)(pz)} n ] 2− . Details of chromate binding by H-bonding based on single-crystal structures of (Bu 4 N) 2 [CrO 4 ⊂ {Cu(OH)(pz)} 28 ], four pseudopolymorphs of (Bu 4 N) 2 [CrO 4 ⊂ {Cu(OH)(pz)} 31 ], and also the methoxy-substituted derivative (Bu 4 N) 2 [CrO 4 ⊂ {Cu 31 (OH) 30 (OCH 3 )(pz) 31 }] are presented.