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1. Supramolecular Incarceration and Extraction of Tetrafluoroberyllate from Water by Nanojars

   https://doi.org/10.1021/acs.inorgchem.2c01198  

   Al Isawi, Wisam A. ; Zeller, Matthias ; Mezei, Gellert ( May 2022 , Inorganic Chemistry)

   The previously unexplored noncovalent binding of the highly toxic tetrafluoroberyllate anion (BeF42–) 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 BeF4-binding propensity of [BeF4⊂{CuII(OH)(pz)}n]2– (pz = pyrazolate; n = 27–32) nanojars of different sizes is investigated using an array of techniques including mass spectrometry, paramagnetic 1H, 9Be, and 19F NMR spectroscopy, and X-ray crystallography, along with thermal stability studies in solution and chemical stability studies toward acidity and Ba2+ ions. The latter is found to be unable to precipitate the insoluble BaBeF4 from nanojar solutions, indicating a very strong binding of the BeF42– anion by nanojars. 9Be and 19F NMR spectroscopy allows for the unprecedented direct probing of the incarcerated anion in a nanojar and, along with 1H 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 (Bu4N)2[BeF4⊂{Cu(OH)(pz)}32], which contains a novel Cux-ring combination (x = 9 + 14 + 9), (Bu4N)2[BeF4⊂{Cu(OH)(pz)}8+14+9], and (Bu4N)2[BeF4⊂{Cu(OH)(pz)}6+12+10] and offers detailed structural parameters related to the supramolecular binding of BeF42– in these nanojars. The extraction of BeF42– 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. 

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2. Selective binding of anions by rigidified nanojars: sulfate vs. carbonate

   https://doi.org/10.1039/d1ob01318a  

   Al Isawi, Wisam A. ; Salome, Austin Z. ; Ahmed, Basil M. ; Zeller, Matthias ; Mezei, Gellert ( September 2021 , Organic & Biomolecular Chemistry)

   Selective binding and transport of highly hydrophilic anions is ubiquitous in nature, as anion binding proteins can differentiate between similar anions with over a million-fold efficiency. While comparable selectivity has occasionally been achieved for certain anions using small, artificial receptors, the selective binding of certain anions, such as sulfate in the presence of carbonate, remains a very challenging task. Nanojars of the formula [anion⊂{Cu(OH)(pz)} n ] 2− (pz = pyrazolate; n = 27–33) are totally selective for either CO 3 2− or SO 4 2− over anions such as NO 3 − , ClO 4 − , BF 4 − , Cl − , Br − and I − , but cannot differentiate between the two. We hypothesized that rigidification of the nanojar outer shell by tethering pairs of pyrazole moieties together will restrict the possible orientations of the OH hydrogen-bond donor groups in the anion-binding cavity of nanojars, similarly to anion-binding proteins, and will lead to selectivity. Indeed, by using either homoleptic or heteroleptic nanojars of the general formula [anion⊂Cu n (OH) n (L2–L6) y (pz) n −2 y ] 2− ( n = 26–31) based on a series of homologous ligands HpzCH 2 (CH 2 ) x CH 2 pzH ( x = 0–4; H 2 L2–H 2 L6), selectivity for carbonate (with L2 and with L4–L6/pz mixtures) or for sulfate (with L3) has been achieved. The synthesis of new ligands H 2 L3, H 2 L4 and H 2 L5, X-ray crystal structures of H 2 L4 and the tetrahydropyranyl-protected derivatives (THP) 2 L4 and (THP) 2 L5, synthesis and characterization by electrospray-ionization mass spectrometry (ESI-MS) of carbonate- and sulfate-nanojars derived from ligands H 2 L2–H 2 L6, as well as detailed selectivity studies for CO 3 2− vs. SO 4 2− using these novel nanojars are presented. 

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3. Isomorphous but No Dead Ringer: Contrasting the Supramolecular Binding of Tetrafluoroberyllate and Sulfate Ions by Nanojars

   https://doi.org/10.1021/acs.cgd.2c01261  

   Al Isawi, Wisam A. ; Zeller, Matthias ; Mezei, Gellert ( March 2023 , Crystal Growth & Design)

   An extensive single-crystal X-ray crystallographic study of 11 nanojar structures (of which seven are novel) of the formula [anion⊂{cis-CuII(μ-OH)(μ-pz)}n]2– (anion = BeF42–, n = 28, 31, 32, CunBeF4; anion = SO42–, n = 28, 31, CunSO4; pz = pyrazolate, C3H3N2–) has been carried out, providing a detailed description of isomorphism and pseudopolymorphism in nanojars. The results point to a remarkable variety in the shape of the constituent [cis-CuII(μ-OH)(μ-pz)]x (Cux; x = 6, 8, 9, 10, 12 and 14) metallamacrocycles, despite only small differences in the coordination environment of the individual Cu2+ centers. The flexibility of the Cux rings and, ultimately, of the nanojar framework allows for the incarceration of different anions with slightly different dimensions in a nanojar of a given size, resulting in the formation of isomorphous structures in the case of CunBeF4 and CunSO4. Selectivity studies monitored by electrospray-ionization mass spectrometry (ESI-MS) and proton nuclear magnetic resonance spectroscopy (1H NMR) reveal that despite the virtually identical H-bonding pattern around the two anions in nanojars of a given size, SO42– is strongly preferred over BeF42–. The origins of this selectivity are discussed, along with the nature of bonding in the two isosteric anions. Lastly, the crystal structure of (Bu4N)3Be2F7(H2O)3 documents the formation of the Be2F73– ion from BeF42–. 

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4. Doubling the Carbonate-Binding Capacity of Nanojars by the Formation of Expanded Nanojars

   https://doi.org/10.3390/molecules26113083  

   Al Isawi, Wisam A. ; Mezei, Gellert ( June 2021 , Molecules)

   null (Ed.)

   Anion binding and extraction from solutions is currently a dynamic research topic in the field of supramolecular chemistry. A particularly challenging task is the extraction of anions with large hydration energies, such as the carbonate ion. Carbonate-binding complexes are also receiving increased interest due to their relevance to atmospheric CO2 fixation. Nanojars are a class of self-assembled, supramolecular coordination complexes that have been shown to bind highly hydrophilic anions and to extract even the most hydrophilic ones, including carbonate, from water into aliphatic solvents. Here we present an expanded nanojar that is able to bind two carbonate ions, thus doubling the previously reported carbonate-binding capacity of nanojars. The new nanojar is characterized by detailed single-crystal X-ray crystallographic studies in the solid state and electrospray ionization mass spectrometric (including tandem MS/MS) studies in solution. 

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5. Absorption spectra of benzoic acid in water at different pH and in the presence of salts: insights from the integration of experimental data and theoretical cluster models

   https://doi.org/10.1039/C9CP06728K  

   Karimova, Natalia V. ; Luo, Man ; Grassian, Vicki H. ; Gerber, R. Benny ( March 2020 , Physical Chemistry Chemical Physics)

   The absorption spectra of molecular organic chromophores in aqueous media are of considerable importance in environmental chemistry. In this work, the UV-vis spectra of benzoic acid (BA), the simplest aromatic carboxylic acid, in aqueous solutions at varying pH and in the presence of salts are measured experimentally. The solutions of different pH provide insights into the contributions from both the non-dissociated acid molecule and the deprotonated anionic species. The microscopic interpretation of these spectra is then provided by quantum chemical calculations for small cluster models of benzoic species (benzoic acid and benzoate anion) with water molecules. Calculations of the UV-vis absorbance spectra are then carried out for different clusters such as C 6 H 5 COOH·(H 2 O) n and C 6 H 5 COO − ·(H 2 O) n , where n = 0–8. The following main conclusions from these calculations and the comparison to experimental results can be made: (i) the small water cluster yields good quantitative agreement with observed solution experiments; (ii) the main peak position is found to be very similar at different levels of theory and is in excellent agreement with the experimental value, however, a weaker feature about 1 eV to lower energy (red shift) of the main peak is correctly reproduced only by using high level of theory, such as Algebraic Diagrammatic Construction (ADC); (iii) dissociation of the BA into ions is found to occur with a minimum of water molecules of n = 8; (iv) the deprotonation of BA has an influence on the computed spectrum and the energetics of the lowest energy electronic transitions; (v) the effect of the water on the spectra is much larger for the deprotonated species than for the non-dissociated acid. It was found that to reproduce experimental spectrum at pH 8.0, additional continuum representation for the extended solvent environment must be included in combination with explicit solvent molecules ( n ≥ 3); (vi) salts (NaCl and CaCl 2 ) have minimal effect on the absorption spectrum and; (vii) experimental results showed that B-band of neutral BA is not sensitive to the solvent effects whereas the effect of the water on the C-band is significant. The water effects blue-shift this band up to ∼0.2 eV. Overall, the results demonstrate the ability to further our understanding of the microscopic interpretation of the electronic structure and absorption spectra of BA in aqueous media through calculations restricted to small cluster models. 

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