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

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.

A highly anisotropic family of hexagonal bipyramidal Dy(iii) unsaturated 18-crown-6 complexes exceeding the blockade barrier over 2700 K: a computational exploration

“…[39][40][41][42][43] Surprisingly, most of the reported [Dy(18C6)X 2 ] + complexes show only moderate barrier heights (∼100 cm −1 ) due to the stabilization of the low-symmetry environment around Dy(III) ions resulting from the high conformational flexibility (C-C bond rotations) in the 18C6 ligands except for a [Dy(O t Bu)Cl(18C6)][BPh 4 ] complex showing a barrier height of ∼1000 K. 22,25,[39][40][41][42][43] In contrast, the unsaturated hexa-18-crown-6 (U18C6) ligands with CvC linkages offer conformation strain and prefer to stabilize the hexagonal bipyramidal environment around metal ions. [44][45][46] Inspired by the exceptionally high coordinating capability of U18C6 towards the isolation of D 6h geometry ( preferable to generate an axial ligand field) and the suitable pore size of 18-crown-6 ligands to stabilize Ln(III) ions, here we investigated the electronic structure and magnetic properties in eleven Dy (III) complexes with the general formula [Dy(U18C6) 1) towards the search of new generation SIMs. All these complexes are named 1 X -5 X (where X = axial ligands, see Table S1 †).…”