Invited lecture: Analysis of frontier orbitals, bonding energy and NMR spectroscopic parameters of actinide-organic complexes through four-component relativistic quantum calculations

AUCAR, GUSTAVO A.

Santa Fe

Workshop; Theory Frontiers in Actinide Science: Chemistry and Materials; 2023

Fundamental knowledge and understanding of actinide bonding trends and coordination modes are significantly limited as compared to other elemental series in the periodic table. There are several and thorough studies involving actinide elements,1 but to our knowledge, there are no studies that use state-of-the-art four-component (4C) relativistic methods for grasping the contribution of f-type atomic orbitals (AOs) in the electronic structures and chemical bonding of actinides (Ac) to medium-size organic ligands. The ability of actinides to form chemical bonds and the role of 5f and 6d AOs in the contribution to molecular orbitals (MO) are still subjects of investigation.2 So, we have recently undertaken a research program whose goals are oriented to learn more about the physics that underlies the structure and electronic properties of actinide-containing complexes, for which relativistic effects must be considered as accurate as possible.In this presentation, we shall show the first results of our research program that were just published.3 We have performed state-of-the-art relativistic calculations at different levels of theory and using local dense basis sets, to investigate the influence of relativistic and electron correlation effects on geometrical structures and bonding energies of Ac-DOPO3 complexes (Ac = Pu, Am, Cf, and Bk); in Figure 1 we show an scheme of the Ac-DOPO3 complex. Two levels were selected: (1) the scalar (sc) and spin?orbit (so) relativistic zeroth order regular approximation (ZORA) within the hybrid density functional theory (DFT) and (2) the 4C Dirac equation with both the Dirac?Hartree?Fock (4C-DHF) and Lévy?Leblond (LL) Hamiltonians.We found that the 5f electrons of those actinides behave differently when relativistic effects are taken into account at different levels of approach, thus changing the frontier MOs of the above mentioned complexes (shown basically in Figure 2 for Am). Furthermore, relativistic effects together with electron correlation modify in a great manner the contribution of 5f- and 6p-AOs, as well as the values of the bonding energies. We shall also show some preliminary results of calculations of NMR spectroscopic parameters on those complexes. We shall consider in its analysis their absolute values and the mechanisms involved. Figure 1: Structure of Ac-DOPO3 complex.Figure 2: Ligand Field Diagram of the Am-DOPO complex calculated at the sr-ZORA/B3LYP, 4C-B3LYP and 4C-DHF levels of theory.References: 1. M. Dolg and X. Cao, Recent Advances in Relativistic Molecular Theory, World Scientific, 2004, vol. 5, 1?36; D. Wang, W. F. van Gunsteren and Z. Chai, Recent Advances in Computational Actinoid Chemistry, Chem. Soc. Rev. 2012, 41, 5836; L. A. Seaman et al., J. Am. Chem. Soc., 2012, 134, 4931?4940; M. P. Kelley et al., J. Am. Chem. Soc., 2017, 139, 9901?9908. 2. M. Tobisu et al., J. Am. Chem. Soc., 2012, 134, 115?118; S. Kundu et al. Organometallics, 2009, 28, 5432?5444. 3. Andy Zapata-Escobar et al., Phys. Chem. Chem. Phys., 2023, Accepted manuscript. https://doi.org/10.1039/D2CP05399C.