Dynamic Characterization of Crystalline Supramolecular Rotors Assembled through Halogen Bonding

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 T1 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.

本研究构建了一套用于制备结晶分子转子的模块化分子套件，该套件由一组定子与转子组成，可便捷获取大量具备不同动态性能与物理特性的目标结构。本工作中，我们以二氮杂双环[2.2.2]辛烷（diaza­bicyclo­[2.2.2]­octane）作为转子，通过其与五种氟代碘苯构成的定子之间的卤键自组装，成功制备得到此类结晶分子转子。通过变温氢-1（¹H）自旋-晶格弛豫T₁测量，我们证实所有结构均展现出超快布朗转动行为，其活化能介于2.4–4.9 kcal/mol，指前因子约为(1–9)×10¹² s⁻¹。针对部分代表性样品的四极回波氘-2（²H）核磁共振线形分析结果表明，其转动轨迹与转子的三重或六重对称势场相一致。