Hydrogen-Bonded Crystalline Molecular Machines with Ultrafast Rotation and Displacive Phase Transitions |
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| Authors: | Abraham Colin-Molina Marcus J. Jellen Dr. Joelis Rodríguez-Hernández Dr. Miguel Eduardo Cifuentes-Quintal Jorge Barroso Dr. Rubén A. Toscano Prof. Gabriel Merino Prof. Braulio Rodríguez-Molina |
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| Affiliation: | 1. Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 Ciudad de México, México;2. Department of Chemistry and Biochemistry, University of California, Los Angeles, California, 90095 USA;3. Centro de Investigación en Química Aplicada (CIQA), Blvd. Enrique Reyna Hermosillo, No. 140, Saltillo, Coahuila, 25294 México;4. Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados, Unidad Mérida. Km 6 Antigua Carretera a Progreso. Apdo. Postal 73, Cordemex, 97310 Mérida, Yuc., México |
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| Abstract: | 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 1H T1 relaxometry experiments indicate very low rotational activation barriers (Ea) of 0.67 kcal mol−1 for 1 and 0.26 kcal mol−1 for 2 , indicating that DABCO can reach a THz frequency at room temperature in the latter. These Ea 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. |
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| Keywords: | displacive phase transitions molecular machines non-covalent interactions relaxation THz frequency |
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