Solvent effects on extractant conformational energetics in liquid-liquid extraction: a simulation study of molecular solvents and ionic liquids

Extractant design in liquid-liquid extraction (LLE) is a research frontier of metal ion separations that typically focuses on the direct extractant-metal interactions. However, a more detailed understanding of energetic drivers of separations beyond primary metal coordination is often lacking, including the role of solvent in the extractant phase. In this work, we propose a new mechanism for enhancing metal-complexant energetics with nanostructured solvents. Using molecular dynamics simulations with umbrella sampling, we find that the organic solvent can reshape the energetics of the extractant's intramolecular conformational landscape. We calculate free energy profiles of different conformations of a representative bidentate extractant, n-octyl(phenyl)-N,N-diisobutyl carbamoyl methyl phosphinoxide (CMPO), in four different solvents: dodecane, tributyl phosphate (TBP), and dry and wet ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]). By promoting reorganization of the extractant molecule into its binding conformation, our findings reveal how particular solvents can ameliorate this unfavorable step of the metal separation process. In particular, the charge alternating nanodomains formed in ILs substantially reduce the free energy penalty associated with extractant reorganization. Importantly, using alchemical free energy calculations, we find that this stabilization persists even when we explicitly include the extracted cation. These findings provide insight into the energetic drivers of metal ion separations and potentially suggest a new approach to designing effective separations using a molecular-level understanding of solvent effects.

Density functional theory (DFT) calculations of VI/V reduction potentials of uranyl coordination complexes in non-aqueous solutions

Of particular interest within the +6 uranium complexes is the linear uranyl(vi) cation and it forms numerous coordination complexes in solution and exhibits incongruent redox behavior depending on coordinating ligands. In this study, to determine the reduction potentials of uranyl complexes in non-aqueous solutions, a hybrid density functional theory (DFT) approach was used in which two different DFT functionals, B3LYP and M06, were applied. Bulk solvent effects were invoked through the conductor-like polarizable continuum model. The solute cavities were described with the united-atom Kohn-Sham (UAKS) cavity definition. Inside the cavity the dielectric constant matches the value of a vacuum and outside the cavity the dielectric constant value is the same as that of the solvent of interest, for example, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dichloromethane (DCM), acetonitrile and pyridine. With the help of the Nernst equation the calculated reduction potentials with respect to the ferrocene (Fc) reference electrode are converted into reduction free energies (RFEs). Uranyl complexes of organic ligands which range from mono- to hexa-dentate coordination modes were investigated in non-aqueous solutions of DMSO, DMF, DCM, acetonitrile and pyridine solutions. The effect of the spin-orbit correction and the reference electrode correction on the RFEs and various methods such as the direct method and the isodesmic reaction model were explored. Overall, our computational determination of RFEs of uranyl complexes in various non-aqueous solutions demonstrates that the RFEs can be obtained within ∼0.2 eV of experimental values.

Aminophosphine Oxides: A Platform for Diversified Functions

This review summarizes significant contributions reported on aminophosphine oxides (AmPOs), specifically those containing at least one amino group present as amino substituents on α- and β-carbons including direct P-N bond containing molecules. AmPOs have additional 'N' site(s), including highly basic 'P=O' groups, and these features make favor smooth and unexpected behavior. The most striking manifestations of flexibility of AmPOs are that they are exciting ligand systems for the coordination chemistry of actinides, and their involvement in catalytic organic reactions including enantioselective opening of meso-epoxides, addition of silyl enol ethers, allylation with allyltributylstannane, etc. The diverse properties of the AmPOs and their metal complexes demonstrate both the scope and complexity of these systems, depending on the basicity of phosphoryl group, and nature of the substituents on the pentavalent tetracoordinate phosphorus atom and metal. Two components key to understanding the challenges of actinide separations are detailed here, namely, previously described separation methods, and recent investigations into the fundamental coordination chemistry of actinides. Both are aimed at probing the critical features necessary for improved selectivity of separations. This review leads to the conclusion that, although many AmPOs have already been discovered and developed over the past century, many opportunities nevertheless exist for further developments towards new extraction processes and new catalytic materials by fine tuning the electronic and steric properties of substituents on the central phosphorus atom.

Bis(cyclo-hexyl-ammonium) tetra-chlorido-diphenyl-stannate(IV)

The title compound, (C6H14N)2[Sn(C6H5)2Cl4], contains cyclo-hexyl-ammonium cations in general positions and a stannate(IV) anion that is located on a twofold rotation axis. The Sn(IV) atom in the complex anion is surrounded by four Cl(-) ligands and two trans-phenyl groups in a distorted octa-hedral configuration. The anions are connected with the cations through N-H⋯Cl hydrogen bonds. Every cation is involved in three N-H⋯Cl bonds to the chloride ligands of three different anions, and each chloride ligand is linked to two cations. This arrangement leads to a layered structure parallel to (010).

Di-chlorido-diphenyl-bis-(thio-urea-κS)tin(IV)

The title compound, [Sn(C₆H₅)₂Cl₂(CH₄N₂S)₂], has been obtained from the reaction between Sn(C₆H₅)₂Cl₂ and SC(NH₂)₂. The asymmetric unit consists of one half of the mol­ecular unit, the remainder generated by a twofold rotation axis located along the Cl—Sn—Cl bonds. The Sn^IV atom is coordinated by two phenyl groups, two Cl atoms and two thio­urea ligands in an all trans octa­hedral C₂Cl₂S₂ environment. Individual mol­ecules are connected through N—H⋯Cl hydrogen bonds, leading to a three-dimensional network structure. Intra­molecular N—H⋯Cl hydrogen bonds are also present.

catena-Poly[[triphenyltin(IV)]-μ-phenylphosphinato-κ2O:O′]

In the structure of the title coordination polymer, [Sn(C₆H₅)₃(C₆H₆O₂P)]_n or [PhP(H)O₂Sn^IV(Ph)₃]_n, the Sn^IV atom is five-coordinate, with the SnC₃O₂ framework in a trans trigonal–bipyramidal arrangement having the PhP(H)O₂⁻ anions in apical positions. In the crystal, neighbouring polymer chains are linked via C—H⋯π inter­actions, forming a two-dimensional network lying parallel to (001).

Dicyclo-hexyl-ammonium trimethyl-bis-(hydrogen phenyl-phospho-nato)stannate(IV)

In the title compound, (C(12)H(24)N)[Sn(CH(3))(3)(C(6)H(6)O(3)P)(2)], the SnMe(3) residues are axially coordinated by two monodentate [PhPO(3)H](-) anions, leading to a trigonal-bipyramidal geometry for the Sn(IV) atom. The two [SnMe(3)(PhPO(3)H)(2)](-) anions in the unit cell are associated into infinite chains along the a axis by O-H⋯O hydrogen bonds involving the hy-droxy group of the hydrogen phenyl-phospho-nate ion. The chains inter-act with one another via O-H⋯O hydrogen bonds along the c axis. These networks of anions assemble with the dicyclo-hexyl-ammonium ion through N-H⋯O hydrogen bonds, forming a three-dimensional network.

A Facile Synthesis of Carbamoylsilanes, -boranes and -phosphane Oxides - Isolation of the First Uncomplexed Carbamoylborane

C-(Trimethylsilyloxy)-, C-(triisopropylsilyloxy)-, C-(diphenylboryloxy), C-[bis(diisopropylamino)boryloxy]- and C-(di-tert-butylphosphoryloxy)-N,N-diisopropylaldiminium salts are readily prepared in good to excellent yields from either diisopropylformamide or (chloromethylene)diisopropylammonium chloride. Deprotonation of these aldiminium salts leads to transient (amino)(oxy)carbenes, which cleanly rearrange to carbamoyl derivatives. This synthetic methodology gives access to sterically hindered carbamoylsilanes, -boranes and phosphane oxides that are hardly accessible by other routes.