Pentafluoroorthotellurate Uncovered: Theoretical Perspectives on an Extremely Electronegative Group

The pentafluoroorthotellurate group (-OTeF₅, teflate) exhibits high electron-withdrawing properties. Indeed, it is often used as a bulky substitute for fluoride due to its high chemical stability and larger size, which reduces its tendency to act as a bridging ligand. These characteristics make it a valuable ligand in synthetic chemistry, facilitating the preparation of molecular structures analogous to polymeric fluoride-based compounds. In this study, we explore the electronic structure of the teflate group by using advanced Quantum Chemical Topology (QCT) methods to better understand its bonding nature and compare its group electronegativity with that of the halogens. For that, we examine XOTeF₅ systems (X = F, Cl, Br, I) and decompose X-OTeF₅ interactions into classical (ionic) and exchange-correlation (covalent) contributions by using interacting quantum atoms (IQA) energy decomposition scheme. We also conduct a detailed analysis of electron distribution by utilizing the statistical framework of electron distribution functions (EDFs) and examine the electron localization function (ELF), electron density, and reduced density gradient scalar functions, as well as delocalization indices and QTAIM charges. The results show that the electron-withdrawing properties of the teflate group are comparable to those of fluorine, albeit slightly lower. Moreover, its internal bonding is primarily ionic. Additionally, we compare -OTeF₅ with other O-donor groups, demonstrating that the electron-withdrawing properties within OEF₅ (E = S, Se, Te) systems are nearly identical, and these groups show a higher group electronegativity than OCF₃, OC(CF₃)₃, and OC₆F₅.