Interplay between the σ-tetrel bond and σ-halogen bond in PhSiF3⋯4-iodopyridine⋯N-base

Abstract

The ternary complexes of PhSiF₃⋯4-iodopyridine⋯N-base (N-base = HCN, NH₃, NHNH₂, and NH₂CH₃), PhTF₃⋯4-iodopyridine⋯NH₃ (T = C and Ge), PhSiY₃⋯4-iodopyridine⋯NH₃ (Y = H and Cl), PhSiF₃⋯4-bromopyridine⋯NH₃ and the respective binary complexes have been investigated. 4-Halopyridine in these ternary complexes plays a dual role of both a Lewis acid with the σ-hole on the halogen atom in the halogen bond and a Lewis base with the nitrogen atom in the tetrel bond. The interplay between both interactions in the ternary complexes has been analyzed in terms of the binding distance, binding energy, charge transfer, electron density and electrostatic potentials. A synergistic effect is found for the tetrel and halogen bonds in most of the ternary complexes, while a diminutive effect is present for the hydrogen and halogen bonds in PhCF₃⋯4-iodopyridine⋯NH₃. The magnitude of cooperative energy depends on the strength of both interactions. Interestingly, PhSiCl₃⋯4-iodopyridine has a stronger tetrel bond than PhSiH₃⋯4-iodopyridine, inconsistent with the size of the σ-hole on the Si atom. In addition, the tetrel bond exhibits a partially covalent interaction nature.