Synthesis and Characterization of Heavy-Metal Oxoanion- and Phosphonate-Binding Nanojars

Date of Award

4-2024

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Gellert Mezei, Ph.D.

Second Advisor

Ekkehard Sinn, Ph.D.

Third Advisor

Andre Venter, Ph.D.

Fourth Advisor

Todd Barkman, Ph.D.

Abstract

Nanojars are an emerging class of anion-binding and extraction agents. These supramolecular coordination complexes (2 nm wide) exhibit exceptional anion binding strength that points to their possible application in the recovery of toxic or valuable anions from water bodies. Nanojars of the formula (TBA)2[XO3/42−⸦{CuII(μ-OH)(μ-pyrazolate)}n] (TBA = tetrabutylammonium cation; XO3/42− = anion; X = Se, Te, Cr, Mo, W, HP, HAs, HV; n = 26 – 36) are synthesized from Cu2+, OH−, pyrazole and the TBA salts of various anions. Nanojars possess hydrophobic exteriors with an array of pyrazolate ligands and hydrophilic interiors with a sequence of hydroxide groups, which make them excellent incarcerating agents for anions with large hydration energy such as SeO42−, CrO42−, MoO42−, WO42−, HPO42−, HAsO42−, HVO42−, SeO32− and TeO32−. One of the challenges in the study of nanojars is the competitive formation of CO32−-incarcerating nanojars due to the carbonate impurities in the reagents or to atmospheric CO2 when subjected to highly basic conditions. Using the polymer [Cu(OH)(pyrazolate)]∞, which already has a deprotonated pyrazolate as well as the OH− molecule needed for the nanojar structure, eliminates the need for additional base during nanojar synthesis, thus reducing the CO32− impurities. Depolymerization of the [trans-Cu(OH)(pyrazolate)]∞ polymer into [cis-Cu(OH)(pyrazolate)]n (n = 27‒32) in the presence of the TBA salt of different anions generates nanojars with no or minimal amounts of CO32− impurities. Characterization was done by electrospray-ionization mass spectrometry, variable-temperature 1H NMR spectroscopy and single-crystal X-ray crystallography.

In addition to inorganic anion pollutants, organic anions such as phosphonates are also ubiquitous in our environment, present in the form of various organophosphorus compounds. These are widely used as scale and corrosion inhibitors, pesticides, bleach-containing detergents, deflocculants, dispersants, and crystal growth modifiers. Nanojars were also synthesized by the two different methods described above to capture phosphonate anions. The phosphonate anions employed feature various small to long alkyl chains as well as aryl groups, including methyl, ethyl, n-propyl, n-butyl, dodecyl, phenyl, and benzyl. Characterization was done by electrospray-ionization mass spectrometry, variable-temperature 1H and 31P NMR spectroscopy, UV-vis spectroscopy and X-ray crystallography. A number of X-ray crystal structures of these novel phosphonate nanojars confirm that the nanojars self-assemble and wrap around the hydrophilic anionic part of the phosphonate and leave the hydrophobic alkyl/aryl part of the anion to string outside the cavity of the nanojar. A novel motif in nanojar chemistry, in which a pair of nanojar molecules is tethered by two phosphonate ligands, termed nanojar clamshell, has also been discovered. Importantly, these clamshell structures double the phosphonate binding capacity of nanojars.

Exploration of the formation of nanojars from copper ions in the presence of various multinuclear metal pyrazolate clusters (with Ni, Fe, Mo, Ti, Sn, Mn) was performed to assess the stability of nanojars relative to other metal pyrazolate clusters. This study specifically focused on the binding affinity of copper to nitrogen and oxygen donors within copper pyrazolate/hydroxide nanojars versus other metal pyrazolate/hydroxide clusters. ESI-MS(−) spectrometry confirmed the conversion of different metal clusters into varying sizes of carbonate nanojars.

This research also considered the potential of nanojars to capture singly-charged anions, which has not been observed yet. In addition to multiple hydrogen bonding interactions within its cavity, enhanced hydrophobic interactions between the nanojar host and the anion guest might lead to the binding of singly-charged anions with aromatic substituents. With that in mind, the substitution of the 4-position of pyrazole with aromatic groups was performed, leading to the synthesis of 4-phenylpyrazole and 4-benzylpyrazole. The substituted pyrazoles were used for the formation of nanojars with increased aromatic outer surface. 1H NMR and ESI-MS(−) were used to characterize the products. The crystal structure of a nanojar based on 4-phenylpyrazole reveals a novel Cu16 central ring, the largest nanojar ring observed so far, sandwiched between two Cu10 side rings.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

4-1-2026

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