Dynamic Characterization of Crystalline Supramolecular Rotors Assembled through Halogen Bonding

Abstract

A modular molecular kit for the preparation of crystalline molecular rotors was devised from a set of stators and rotators to gain simple access to a large number of structures with different dynamic performance and physical properties. In this work, we have accomplished this with crystalline molecular rotors self-assembled by halogen bonding of diaza­bicyclo­[2.2.2]­octane, acting as a rotator, and a set of five fluorine-substituted iodo­benzenes that take the role of the stator. Using variable-temperature ¹H <i>T</i>₁ spin–lattice relaxation measurements, we have shown that all structures display ultrafast Brownian rotation with activation energies of 2.4–4.9 kcal/mol and pre-exponential factors of the order of (1–9) × 10¹² s^–1. Line shape analysis of quadrupolar echo ²H NMR measurements in selected examples indicated rotational trajectories consistent with the 3-fold or 6-fold symmetric potential of the rotator