QTAIM analysis of a [2]rotaxane molecular shuttle with a 2,2'-bipyridyl rigid core.

Abstract

Chemical contacts responsible for the supramolecular assembly of a rigid H-shaped [2]rotaxane molecular shuttle composed by a 24-crown-8(24C8) macrocycle on a molecular thread containing two benzimidazole (Bzi) recognition sites and a central 2,2'-bipyridyl (Bipy) rigid core are analytically addressed combining Quantum Theory of Atoms in Molecules (QTAIM) with Density Functional Theory (DFT). In this respect, the available crystallographic structure - CCDC number 2248267 - is taken as a reference condition for addressing the nature of the chemical interactions finely modulating the shuttling of the 24C8 between Bzi stations. Moreover, previous DFT computations (Chem. Sci., 2023, 14, 7215) are extended over a supercomputing environment to address the proposed ligand exchange mechanism involving DMF solvent molecules and promoting the observed shuttling process upon the addition of Zn(II) cations. To this end, converged DFT wavefunctions are fully analyzed by means of electron density ρ(r) and local electronic energy density - H(r) - descriptors; interestingly, the derived covalent vs non-covalent interaction patterns shed some light on the mutual position of the macrocycle along the axle following the coordination of Zn(II) ions in DMF solvent.