Towards a Stronger Halogen Bond Involving Astatine: Unexpected Adduct with Bu₃PO Stabilized by Hydrogen Bonding

Abstract

The halogen bond is a powerful tool for the molecular design and pushing the limits of its strength is of major interest. Bearing the most potent halogen‐bond donor atom, astatine monoiodide (AtI) was recently successfully probed [Nat. Chem. 2018, 10, 428–434]. In this work, we continue the exploration of adducts between AtI and Lewis bases with the tributylphosphine oxide (Bu3PO) ligand, revealing the unexpected experimental occurrence of two distinct chemical species with 1:1 and 2:1 stoichiometries. The 1:1 Bu3PO⋅⋅⋅AtI complex is found to exhibit the strongest astatine‐mediated halogen bond so far (with a formation constant of 10(4.24±0.35)). Quantum chemical calculations unveil the intriguing nature of the 2:1 2Bu3PO⋅⋅⋅AtI adduct, involving a halogen bond between AtI and one Bu3PO molecular unit plus CH⋅⋅⋅O hydrogen bonds chelating the second Bu3PO unit.

Quantum chemical topology at the spin–orbit configuration interaction level: Application to astatine compounds

“…Note that some of these systems exist in solution [32,33] and have attracted a strong interest in the field of halogen-bond interactions. [34,35] 2 | THEORY AND METHODS…”

An expanded halogen bonding scale using astatine

“…Among the halogens, we confirmed the highest donating ability of astatine, especially compared to iodine. 17,18 There are fundamental interests to get more experimental data, not only in order to confirm previous findings, but also to increase our understanding of halogen bonding from the perspective of the most potent halogen element, in particular for the refinement of theoretical models. 19,20 On the other hand, the 211 radioisotope of astatine presents potential use in targeted therapy of cancers.…”

“…compounds by studying the distribution of 211 At radionuclide in biphasic liquid systems. 17,18,30,31,33 However, a careful selection of the XB donor and acceptors was mandatory to guarantee the occurrence of XB interactions. Among the dihalogens with strong potent donor ability, 34 the At 2 and AtF species are still hypothetical.…”

Halogen-Bonded Guanine Base Pairs, Quartets and Ribbons

“…The first experimental evidence of halogen bonding with astatine was provided in 2018 [35]. In 2020, a coupled experimental and computational approach identified a 1:1 adduct of Bu 3 PO•••AtI as the strongest astatine-mediated halogen bond found so far [36]. Table 1 compares the interaction energies and selected geometrical parameters calculated at different levels of theory for the I1,I2-substituted R-I dimer.…”

“…The first experimental evidence of halogen bonding with astatine was provided in 2018 [ 35 ]. In 2020, a coupled experimental and computational approach identified a 1:1 adduct of Bu 3 PO•••AtI as the strongest astatine-mediated halogen bond found so far [ 36 ].…”