Synthesis and Studies of Ferroelectric Metal-Organic Cages and Frameworks .

Abstract

Ferroelectric properties derived from the metal-organic assemblies have attracted significant attention as an alternate choice of the conventional inorganic ceramics due to their fascinating structural architectures, simple protocol of synthesis and no potential toxic elements. Here, a new discrete octahedral metal-organic cage [Cu6(H2O)12(TPPA)8].(NO3)12.(H2O)24 has been synthesized using a flexible tripodal ligand TPPA (TPPA=tris(3-pyridinyl) phosphoric triamide). SCXRD analysis reveals that the cage is crystallized in non-centrosymmetric polar space group (I4) which is suitable to show ferroelectric behaviour. Ferroelectric measurements were performed on the powder pressed pellet at room temperature on the Sawyer-Tower circuit. The well resolved rectangular P-E hysteresis loop was obtained exhibiting high remnant polarization (Pr) of 39.23µCcm-2 at 0.1 Hz. The switching rate strongly affects the dynamics of the domain walls which is clearly reflected in the frequency-dependent studies of P-E loop which shows a significant decrease in the Pr values when increasing the AC frequency. The ferroelectric response is due to the ordering of disordered nitrate ions and solvate molecule which is present between the pockets of the cages. Solvent dependent studies confirm the reversible nature of desolvation and resolvation in this cage.