Unsaturated Sulfur Crown Ethers Can Extract Mercury(II) and Show Promise for Future Copernicium(II) Studies: A Combined Experimental and Computational Study

Maryline G Ferrier; Carlos A Valdez; Saurabh Kumar Singh; Saphon Hok; Debmalya Ray; Laura Gagliardi; John D Despotopulos

doi:10.1021/acs.inorgchem.1c01869

Unsaturated Sulfur Crown Ethers Can Extract Mercury(II) and Show Promise for Future Copernicium(II) Studies: A Combined Experimental and Computational Study

Inorg Chem. 2022 Jan 17;61(2):807-817. doi: 10.1021/acs.inorgchem.1c01869. Epub 2021 Dec 29.

Authors

Maryline G Ferrier¹, Carlos A Valdez^{1

2}, Saurabh Kumar Singh³, Saphon Hok^{1

2}, Debmalya Ray⁴, Laura Gagliardi^{5

6}, John D Despotopulos¹

Affiliations

¹ Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, California 94550, United States.
² Forensic Science Center, Lawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, California 94550, United States.
³ Department of Chemistry, Indian Institute of Technology (IIT) Hyderabad, Kandi, Sangareddy 502285, Telangana, India.
⁴ Department of Chemistry, Chemical Theory Center and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.
⁵ Department of Chemistry, Pritzker School of Molecular Engineering, James Franck Institute, Chicago Center for Theoretical Chemistry, The University of Chicago, 5735 S Ellis Avenue, Chicago, Illinois 60637, United States.
⁶ Argonne National Laboratory, 97000 South Cass Avenue, Lemont, Illinois 60439, United States.

PMID: 34965111
DOI: 10.1021/acs.inorgchem.1c01869

Abstract

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.