Benzothiadiazole-based rotation and possible antipolar order in carboxylate-based metal-organic frameworks

By modifying organic ligands of metal-organic framework with dipolar units, they turn suitable for various applications, e.g., in the field of sensor systems or switching of gas permeation. Dipolar linkers in the organic ligand are capable to rotate in certain temperature and frequency ranges. The copper-bearing paddlewheel shaped metal-organic frameworks ZJNU-40 and JLU-Liu30 possess such a polarizable dipole moment due to their benzothiadiazole moiety in the organic ligands. Here, we investigate the molecular rotor behavior of benzothiadiazole units of the two carboxylate-based MOFs by dielectric spectroscopy and computational simulation. Our dielectric results provide clear evidence for significant reorientational relaxation dynamics of these rotors, revealing various characteristics of glasslike freezing upon cooling. The calculated rotational energy barriers are consistent with experimentally determined barriers for single-dipole dynamics. Moreover, for JLU-Liu30 we find hints at antipolar ordering below about 300 K. Metal-organic frameworks containing rotatable dipolar linkers are of interest for sensor systems and in gas separation. Here, the authors investigate the molecular rotor behaviour of benzothiadiazole units in the carboxylate-based MOFs ZJNU-40 and JLU-Liu30 using dielectric spectroscopy and computational simulations.

Automated summary

By modifying the organic ligands of metal-organic framework with dipolar units, they can be used in various applications such as sensor systems and gas permeation switching. The dipolar linkers in the organic ligands can rotate within specific temperature and frequency ranges. Through dielectric spectroscopy and computational simulation, the authors investigate the behavior of benzothiadiazole units in the carboxylate-based MOFs ZJNU-40 and JLU-Liu30, revealing significant reorientational relaxation dynamics and glasslike freezing characteristics upon cooling. Metal-organic frameworks containing rotatable dipolar linkers are important for sensor systems and gas separation.