The effect of frustrated Lewis donors
on metal selectivity between
actinides and lanthanides was studied using a series of novel organic
ligands. Structures and thermodynamic energies were predicted in the
gas phase, in water, and in butanol using 9-coordinate, explicitly
solvated (H2O) Eu, Gd, Am, and Cm in the +III oxidation
state as reactants in the formation of complexes with 2-(6-[1,2,4]-triazin-3-yl-pyridin-2-yl)-1H-indole (Core 1), 3-[6-(2H-pyrazol-3-yl)pyridin-2-yl]-1,2,4-triazine
(Core 2), and several derivatives. These complexations were studied
using density functional theory (DFT) incorporating scalar relativistic
effects on the actinides and lanthanides using a small core pseudopotential
and corresponding basis set. A self-consistent reaction field approach
was used to model the effect of water and butanol as solvents. Coordination
preferences and metal selectivity are predicted for each ligand. Several
ligands are predicted to have a high degree of selectivity, particularly
when a low ionization potential in the ligand permits charge transfer
to Eu(III), reducing it to Eu(II) and creating a half-filled f7 shell. Reasonable separation is predicted between Cm(III)
and Gd(III) with Core 1 ligands, possibly due to ligand donor frustration.
This separation is largely absent from Core 2 ligands, which are predicted
to lose their frustration due to proton transfer from the 2N to the
3N position of the pyrazole component of the ligands via tautomerization.