Computational Study of Actinyl Ion Complexation with Dipyriamethyrin Macrocyclic Ligands

Abstract

Relativistic density functional theory has been employed to characterize [AnO2(L)]0/‑1 complexes, where An = U, Np, Pu, and Am, and L is the recently reported hexa-aza porphyrin analogue, termed dipyriamethyrin, which contains six nitrogen donor atoms (four pyrrolic and two pyridine rings). Shorter axial (AnO) and longer equatorial (An–N) bond lengths are observed when going from AnVI to AnV. The actinide to pyrrole nitrogen bonds are shorter as compared to the bonds to the pyridine nitrogens; the former also play a dominant role in the formation of the actinyl (VI and V) complexes. Natural population analysis shows that the pyrrole nitrogen atoms in all the complexes carry higher negative charges than the pyridine nitrogens. Upon binding actinyl ions with the ligand a significant ligand-to-metal charge transfer takes place in all the actinyl (VI and V) complexes. The formation energy of the actinyl­(VI,V) complexes in the gas-phase is found to decrease in the order of UO2L > PuO2L > NpO2L > AmO2L. This trend is consistent with results for the formation of complexes in dichloromethane solution. The calculated ΔG and ΔH values are negative for all the complexes. Energy decomposition analysis (EDA) indicates that the interactions between actinyl­(V/VI) and ligand are mainly controlled by electrostatic components over covalent orbital interactions, and the covalent character gradually decreases from U to Am for both pentavalent and hexavalent actinyl complexes.

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed “Breaks”?

“…Quantifying the extent of covalent bonding involving the actinide (An) 5f shell and different donor ligands is at the forefront of actinide chemistry research. − Actinide selectivity of extraction reagents is typically associated with a degree of 5f covalent bonding when compared to 4f bonding of the lanthanide (Ln) analogues. − Identifying and quantifying covalency in the An–ligand bonding is therefore essential for solving practical problems encountered, for instance, in the nuclear fuel cycle. − 5f covalency is also a fascinating topic on its own that has attracted much interest in the chemistry community, as evidenced by many publications (refs − and other articles cited herein represent a selection).…”

X-ray absorption spectra of f-element complexes: insight from relativistic multiconfigurational wavefunction theory

“…The contraction was proven to be driven by the decrease in the ionic radius. [154][155][156] Other studies indicated increasing 5f covalency in the An-O yl bonds toward Pu. [157][158][159] Calculated and experimental XANES spectra are shown in Fig.…”

Chemical bonding in actinyl(v/vi) dipyriamethyrin complexes for the actinide series from americium to californium: a computational investigation

“…53,54 We have recently reported the favorable bonding features between dipyriamethyrin and other AnO 2 n + (An = Np, Pu and Am; n = 1, 2) ions in gaseous and CH 2 Cl 2 media. 55 However, the understanding of the complexing ability of the dipyriamethyrin ligand with minor actinides as dioxocations remains unexplored.…”