Accurate Evaluation of Dispersion Energies at Coupled Cluster Level to Understand the Substituent Effects in Am(III) and Eu(III) Complexes

Abstract

The effect of cyclic and aromatic substituents on the complexation behavior of phosphine oxide ligands with Am(III) and Eu(III) was investigated at density functional theory (DFT) and domain-based local pair natural orbital coupled-cluster (DLPNO–CC) levels. Combining DFT with accurate coupled cluster methods, we have evaluated the dispersion energy contributions to the complexation energies for trivalent Am and Eu complexes for the first time. Irrespective of the nature of substituents on the P atom, the electronic structure of the PO group remains identical in all of the ligands. The study reveals the importance of dispersion interactions during complexation and is estimated to be more significant for Am(III) than for Eu(III) complexes.

Understanding the Complexation Behavior of Carbamoylphosphine Oxide Ligands with Representative f-Block Elements

“…Therefore, only complexes with PO group coordination are considered for the monodentate ligand complexes. The complexes formed by CMPO ligands in 1:1 and 1:2 ratios have also been investigated in previous studies. , Due to the large size of the molecular systems and marginal sensitivity of the geometries to the basis set changes, , the geometry optimizations of the metal complexes were exclusively carried out at the RI-BP86-D3BJ/def2-TZVP-ECP level.…”

“…Subsequent calculations derived a septet ground state for Am­(NO 3 ) 3 , Eu­(NO 3 ) 3 , and their complexes. Experimental and theoretical evidence has shown trivalent lanthanide and actinide ions show similar coordination behavior, and their nitrates form 1:3 complexes with CMPO ligands. ,,,,,, Therefore, detailed investigations were focused solely on the 1:3 complexes of L 1 . The geometries of the 1:1 and 1:2 complexes are discussed in the electronic Supporting Information; see Figures S2–S3 and Table S4.…”

“…This discrepancy once again emphasizes the importance of including dispersion interactions during optimization and when computing complexation energies. In a recent study, we proposed a combined DFT and DLPNO–CCSD approach to accurately estimate the complexation energy for trans-plutonium complexes, including dispersion energy contribution . Unfortunately, the DLPNO–CCSD computations are expensive, and for the systems considered in this study, these computations are presently beyond the reach of our computational resources.…”

“…A triple-ζ basis set with two sets of polarization functions (TZ2P) was used for all of the atoms during this step. Note that the use of the BP86 functional for the EDA of lanthanide and actinide complexes is well documented. ,,, During the EDA computations, a two-fragment scheme was adopted with the metal nitrate forming one fragment and the ligands constituting the second fragment. Since our focus is on the interaction between the metal nitrate and the ligand at the interface of the aqueous and organic layers, leading to complexation, cation–cation (metal ion) and cation–anion (metal ion and nitrate ion) interactions are not explored in this work.…”