Ferroelectricity through Reversible Anion-Relay Polarization Switching in a Two-Dimensional Metal–Organic Framework

Ferroelectric materials are central to next-generation electronics and energy technologies because of their ability to couple electrical, mechanical, and thermal signals. Metal–organic frameworks (MOFs) provide a versatile platform for such functionalities owing to their structural tunability; however, despite notable examples, the microscopic mechanisms governing polarization switching in MOFs remain poorly understood. Here we report a Cu(II)-based polar two-dimensional metal–organic framework Cu(PhPO(NHCH 2 3 Py) 2 )(NO 3 ) 2 ·2H 2 O ( 1·2H 2 O ), constructed from a low-symmetric flexible dipodal phosphoramide ligand, PhPO(NHCH 2 3 Py) 2 . Compound 1·2H 2 O exhibits robust ferroelectricity, confirmed by a well-defined rectangular P – E hysteresis loop with a saturation polarization of 1.2 μC/cm 2 . The ferroelectric polar domains, along with bias-dependent amplitude-butterfly and phase-hysteresis loops, were characterized by piezoresponse force microscopy (PFM). First-principles calculations uncover an unusual displacive polarization-switching pathway, in which two nitrate ions displace together along a field-defined direction, enabling reversible 180° dipole reversal through bonding reorganization at the Cu(II) center. This reversible anion-relay mechanism expands the catalog of microscopic ferroelectric processes and represents a new paradigm for MOFs. To demonstrate practical utility, flexible piezoelectric nanogenerators (PENGs) were fabricated by embedding 1·2H 2 O in thermoplastic polyurethane composites. The champion 10 wt % device delivered an open-circuit voltage of 25.1 V and a maximum power density of 48.7 μW/cm 2 , highlighting the potential of MOF-based ferroelectrics for piezoelectric energy harvesting applications. This publication is licensed under You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator. *Disclaimer This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator. *Disclaimer This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator. *Disclaimer This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.