The traditional concept of covalency, introduced by Lewis in 1919, which refers to the sharing of electron pairs between atoms, is still subject of study. Back in those days, ionic bonds were understood as the opposite of covalent bonds, while recently it has been proven that both can be combined to form the so-called polar bonds. The chemical bond in actinides has been demonstrated to be mostly dominated by ionic interactions, with covalent contributions depending on the actinide center and the properties of the ligands. Thus, differences in covalency among actinides have a pivotal role in expanding our knowledge of fundamental chemistry and also for applied chemistry such as separation techniques. One way to approach covalency from theory is through energy decomposition analyses, where the molecule is split up into two separate fragments to assess the contributions coming from each part to form the chemical bond. While most of the partitioning schemes are based on chemical intuition, the Interacting Quantum Atom (IQA) energy decomposition theory relies on the natural partition provided by the Quantum Theory of Atoms in Molecules (QTAIM) within the topological atom framework. In this study, we focused on An – X (X = O, N, S) bonds where IQA was used to assess covalency through differences in correlation and exchange interactions. Our results allow us to explain the differences in covalency between early and late actinides, the role of the ligands, and how different oxidation states can modulate the covalent character of a complex.

Understanding chemical bonds in actinide complexes through the interacting quantum atom energy decomposition analysis

2019 Spring National Meeting

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