Unsaturated Sulfur Crown Ethers Can Extract Mercury(II)
and Show Promise for Future Copernicium(II) Studies: A Combined Experimental
and Computational Study
posted on 2021-12-29, 18:07authored byMaryline
G. Ferrier, Carlos A. Valdez, Saurabh Kumar Singh, Saphon Hok, Debmalya Ray, Laura Gagliardi, John D. Despotopulos
The
unsaturated hexathia-18-crown-6 (UHT18C6) molecule was investigated
for the extraction of Hg(II) in HCl and HNO3 media. This
extractant can be directly compared to the recently studied saturated
hexathia-18-crown-6 (HT18C6). The default conformation of the S lone
pairs in UHT18C6 is endodentate, where the pocket of the charge density,
according to the crystal structures, is oriented toward the center
of the ring, which should allow better extraction for Hg(II) compared
to the exodentate HT18C6. Batch study experiments showed that Hg(II)
had better extraction at low acid molarity (ca. 99% in HCl and ca.
95% in HNO3), while almost no extraction was observed above
0.4 M HCl and 4 M HNO3 (<5%). Speciation studies were
conducted with the goal of delineating a plausible extraction mechanism.
Density functional theory calculations including relativistic effects
were carried out on both Hg(II)-encapsulated HT18C6 and UHT18C6 complexes
to shed light on the binding strength and the nature of bonding. Our
calculations offer insights into the extraction mechanism. In addition
to Hg(II), calculations were performed on the hypothetical divalent
Cn(II) ion, and showed that HT18C6 and UHT18C6 could extract Cn(II).
Finally, the extraction kinetics were explored to assess whether this
crown can extract the short-lived Cn(II) species in a future online
experiment.