Chalcogen Bonding with Diaryl Ditellurides: Evidence from Solid State and Solution Studies.

The chalcogen bonding (ChB) ability of Te is studied in symmetrical diaryl ditellurides ArTeTeAr. Among the two Te σ-holes, the one along the less polarized Te−Te bond was calculated as the more electropositive. This counter-intuitive situation is due to the hyperconjugation contribution from Te lone pair to the σ* of the adjacent Te which coincides with σ-hole along the more polarized Te−Ar bond. ArTeTeAr showed notable structural features in the solid state as a result of intermolecular Te⋅⋅⋅Te ChB, such as a Te₄ rectangle through dimer aggregation or a triangular Te₃ motif, where one Te interacts with both Te atoms of a neighboring molecule through both its σ-hole and lone pair, in a slightly frustrated geometry. Lewis acidity of ArTeTeAr was also evaluated by NMR with R₃PO as σ-hole acceptors in different solvents. Thus, ¹²⁵Te NMR allowed monitoring Te⋅⋅⋅O interaction and delivering association constants (K_a) for 1 : 1 adducts. The highest value of K_a=90 M⁻¹ was measured for the adduct between ArTeTeAr bearing CF₃ groups and Et₃PO in cyclohexane. Notably, by using nBu₃PO, Te⋅⋅⋅O interaction was revealed by ¹⁹F-¹H HOESY showing spatial proximity between CF₃ and CH₃ of nBu₃PO.