The Chemical Bond at the Bottom of the Periodic Table: The Case of the Heavy Astatine and the Super‐Heavy Tennessine

Abstract

AbstractIn this work, we study the chemical bond in molecules containing heavy and super‐heavy elements according to the current state‐of‐the‐art bonding models. An Energy Decomposition Analysis in combination with Natural Orbital for Chemical Valence (EDA‐NOCV) within the relativistic four‐component Dirac‐Kohn‐Sham (DKS) framework is employed, which allows to successfully include the spin‐orbit coupling (SOC) effects on the chemical bond description. Simple halogen‐bonded adducts ClX⋯L (X=At, Ts; L=NH3, Br−, H2O, CO) of astatine and tennessine have been selected to assess a trend on descending along a group, while modulating the ClX⋯L bond features through the different electronic nature of the ligand L. Interesting effects caused by SOC have been revealed: i) a huge increase of the ClTs dipole moment (which is almost twice as that of ClAt), ii) a lowering of the ClX⋯L bonding energy arising from different contributions to the ClX…L interaction energy strongly depending on the nature of L, iii) a quenching of one of the π back‐donation components to the bond. In the ClTs(CO) adduct, the back‐donation from ClTs to CO becomes the most important component. The analysis of the electronic structure of the ClX dimers allows for a clear interpretation of the SOC effects in these systems.