Colin-Molina Abraham, Jellen Marcus J, Rodríguez-Hernández Joelis, Cifuentes-Quintal Miguel Eduardo, Barroso Jorge, Toscano Rubén A, Merino Gabriel, Rodríguez-Molina Braulio
Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510, Ciudad de México, México.
Department of Chemistry and Biochemistry, University of California, Los Angeles, California, 90095, USA.
Chemistry. 2020 Sep 10;26(51):11727-11733. doi: 10.1002/chem.202001156. Epub 2020 Aug 7.
Two new crystalline rotors 1 and 2 assembled through N-H⋅⋅⋅N hydrogen bonds by using halogenated carbazole as stators and 1,4-diaza[2.2.2]bicyclooctane (DABCO) as the rotator, are described. The dynamic characterization through H T relaxometry experiments indicate very low rotational activation barriers (E ) of 0.67 kcal mol for 1 and 0.26 kcal mol for 2, indicating that DABCO can reach a THz frequency at room temperature in the latter. These E values are supported by solid-state density functional theory computations. Interestingly, both supramolecular rotors show a phase transition between 298 and 250 K, revealed by differential scanning calorimetry and single-crystal X-ray diffraction. The subtle changes in the crystalline environment of these rotors that can alter the motion of an almost barrierless DABCO are discussed here.
本文描述了两种新型晶体转子1和2，它们通过N-H⋅⋅⋅N氢键组装而成，使用卤代咔唑作为定子，1,4-二氮杂[2.2.2]双环辛烷（DABCO）作为转子。通过HT弛豫测量实验进行的动态表征表明，转子1的旋转活化能垒（E）非常低，为0.67 kcal mol，转子2的为0.26 kcal mol，这表明在后者中DABCO在室温下可以达到太赫兹频率。这些E值得到了固态密度泛函理论计算的支持。有趣的是，通过差示扫描量热法和单晶X射线衍射揭示，两种超分子转子在298和250 K之间都表现出相变。本文讨论了这些转子晶体环境中的细微变化，这些变化可以改变几乎无势垒的DABCO的运动。
