Trends in Methanol-Solvated Actinide Ions and Actinide Expanded Porphyrin Complexes

Trivalent actinide expanded porphyrin complexes have been of synthetic interest since the isolation of the series of trivalent lanthanide texaphyrin complexes in 1992, however, synthesis of these actinide-based complexes has not yet been achieved. In this work, a computational study with relativistic density functional theory was performed to determine how trivalent actinide ions (Ac³⁺ through Lr³⁺) interact with Schiff base expanded porphyrin macrocycles in a methanol solvent as an alternate pathway to stabilization. A thorough analysis of structural parameters, electronic structure, stability of microsolvation environments, and relative binding energies provided insight into the most stable structures. Trends in bonding and structure for the full actinide series are reported for methanol solvated ions, which reports actinide contraction along the series for early and mid actinides. Texaphyrin incorporates the actinide ions in a planar fashion, whereas for alaskphyrin a bent structure is more favorable; this bend results in stronger interaction energies than those calculated for the texaphyrin complexes. We also show that the redox-active expanded porphyrin ligands are able to accommodate a variety of actinides through charge transfer stabilization. Based on relative binding energy and energy decomposition analysis, it was found that texaphyrin and alaskaphyrin both exhibit a strong preference for binding to Th.