Ferroelectric Behavior of an Octahedral Metal-Ligand Cage and Its 2D-Connected Cage Framework.

Supramolecular systems hold great potential as ferroelectric materials because they are easy to prepare and do not require toxic and environmentally damaging elements. However, directing the self-assembly process of a supramolecular array to yield polarizable solids is still challenging. Here, we describe induced ferroelectricity in a supramolecular framework of metal-organic cages that are supported by a flexible tripodal ligand (NHCH2 -(3-Py))3 PO (TPPA). Ferroelectric responses on the discrete cage [Cu6 (H2 O)12 (TPPA)8 ](NO3 )12  ⋅ 45H2 O (1) and its 2D-connected framework [{Cu6 Cl4 (H2 O)6 (TPPA)8 }(NO3 )8  ⋅ 60H2 O]n (2) yielded well-resolved rectangular hysteresis loops at room temperature with remnant polarization values of 27.27 and 29.09 μC/cm2 , respectively. Thermal hysteresis measurements (THM) and capacitance-voltage (C-V) plots further corroborate the ferroelectric behavior in these compounds. The polarization in them is due to the displacements of solvated molecules and nitrate ions in the pockets of these frameworks.