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

Abstract

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 (NHCH 2-(3-Py)) 3 PO (TPPA). Ferroelectric responses on the discrete cage [Cu 6 (H 2 O) 12 (TPPA) 8 ](NO 3) 12 • 45H 2 O (1) and its 2D-connected framework [{Cu 6 Cl 4 (H 2 O) 6 (TPPA) 8 }(NO 3) 8 • 60H 2 O] n (2) yielded well-resolved rectangular hysteresis loops at room temperature with remnant polarization values of 27.27 and 29.09 μC/cm 2 , respectively. Thermal hysteresis measurements (THM) and capacitance-voltage (CÀ 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.

Strategies for the Construction of Functional Materials Utilizing Presynthesized Metal‐Organic Cages (MOCs)

“…Such sites may be empty or occupied by liable solvent molecules in the MOCs. Using inorganic ligands, a recent report indicated a Cu‐MOC can be linked to a 2D network by Cl − anions via the addition of NaCl to the MOC solution for five days [43] . Most works based on this strategy use organic linkers.…”

“…Using inorganic ligands, a recent report indicated a Cu-MOC can be linked to a 2D network by Cl À anions via the addition of NaCl to the MOC solution for five days. [43] Most works based on this strategy use organic linkers. The first work was reported by Zhou and co-workers [25] in 2009, describing the stepwise synthesis of MOFs based on a soluble octahedral MOC-16 as a precursor.…”

Flexible Piezoelectric Nanogenerators Based on One-Dimensional Neutral Coordination Network Composites

“…However, unlike traditional all-inorganic materials, it is challenging to impart ferroelectricity to the metal–ligand systems as structure–function relationships for them can only be drawn tentatively. , Despite the lack of highly dependable design rules, polar order in coordination networks can be achieved preferentially by systematic tuning of the nature of metal ions, coordinating ligands, counterions, and guest molecules. ,, However, attaining ferroelectricity in neutral framework materials derived from carboxylate-based ligands has thus far been a challenging task; hence, such systems are far less explored than those with charged networks. The polarity in neutral MOFs can be induced by the incorporation of polar functional groups in carboxylate ligands or via encapsulation of polar solvent molecules like water and DMF ( N , N -dimethylformamide), which interacts with the frameworks via non-covalent interactions. ,− Our group has been engaged in the design efforts of polar metal–ligand materials based on pyridyl donor ligands such as [PhPO­(NHPy) 2 ], (Py = 3-pyridyl ( 3 Py) or 4-pyridyl ( 4 Py)), [PS­(NH 3 Py) 3 ], and [PO­(NHCH 2 3 Py) 3 ], in which the piezo- and ferroelectricity originate from their stable charge-separated structure and the low symmetry of the employed phosphoramide scaffold. − Hence, we reasoned that developing pseudo-C 2 and C 3 symmetric phsosphoramide ligands containing carboxylic acid functional groups would result in the generation of neutral noncentrosymmetric coordination networks suitable for ferro- and piezoelectric studies. In this contribution, we describe a new neutral one-dimensional zinc coordination network {[Zn­( L 1 )­(bpy)]·(H 2 O) 1.5∞ } ( 1 ), employing the flexible carboxylate functionalized dipodal P-N ligand [PhPO­(NH-(C 6 H 4 COOH)) 2 ] ( L 1 H 2 ), which crystallizes in the polar non-centrosymmetric space group R 3 c .…”

Visualization of domain structure and piezoelectric energy harvesting in a ferroelectric metal–ligand cage

“…Our group has been interested in the design of ferroelectric [M II 6 L 8 ] 12+ type metal-ligand octahedral cages supported by tripodal N-donor ligands. [13][14][15] Though the ferroelectricity in these axially symmetric cages was probed by typical P-E hysteresis loop measurements, visualization of ferroelectric domain structures and piezoelectric energy harvesting on their thin films were not explored until now.…”