Hydrogen-Bonded Ferroelectrics Based on Metal−Organic Coordination

Biodegradable ferroelectric molecular crystal with large piezoelectric response

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 × 10-3 volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.

Physicochemical Properties of Organic Molecular Ferroelectric Diisopropylammonium Chloride Thin Films

We fabricated ferroelectric films of the organic molecular diisopropylammonium chloride (DIPAC) using the dip-coating technique and characterized their properties using various methods. Fourier-transform infrared, scanning electron microscopy, and X-ray diffraction analysis revealed the structural features of the films. We also performed ab-initio calculations to investigate the electronic and polar properties of the DIPAC crystal, which were found to be consistent with the experimental results. In particular, the optical band gap of the DIPAC crystal was estimated to be around 4.5 eV from the band structure total density-of-states obtained by HSE06 hybrid functional methods, in good agreement with the value derived from the Tauc plot analysis (4.05 ± 0.16 eV). The films displayed an island-like morphology on the surface and showed increasing electrical conductivity with temperature, with a calculated thermal activation energy of 2.24 ± 0.03 eV. Our findings suggest that DIPAC films could be a promising alternative to lead-based perovskites for various applications such as piezoelectric devices, optoelectronics, sensors, data storage, and microelectromechanical systems.

Magneto-Electric Directional Anisotropy in Polar Soft Ferromagnets of Two-Dimensional Organic-Inorganic Hybrid Perovskites

Two-dimensional organic-inorganic hybrid perovskites (2D-OIHPs) are attracting interest due to their structural tunability and rich functional characteristics, such as ferroelectricity and ferromagnetism. Here, we report the chiral-polar ferromagnetic 2D-OIHP copper chlorides with discernable electric polarization in the inorganic layers. In these systems, the magneto-electric (ME) correlation has been clearly observed by measuring a magneto-electric directional anisotropy (MEA), in which an optical absorption coefficient changes with reversal of the light propagating direction. We have found that the MEA can be induced by a low magnetic field of about 50 mT, reflecting soft magnetic nature. The present results suggest a new paradigm for designing functional ME multiferroics, which effectively couples magnetic and electric properties.

One-dimensional DABCO hydrogen-bonding chain in a hexagonal channel of magnetic [Ni(dmit)2]

Crystals of (HDABCO+)9(DABCO)[Ni(dmit)2]9·6CH3CN were shown to have a space group of R3[combining macron], a hexapetal flower-like channel of [Ni(dmit)2] anions, and a one-dimensional hydrogen bonding chain composed of protonated DABCO and CH3CN molecules. The crystals display antiferromagnetic and ferromagnetic interactions within and between hexamers, respectively, whereas the flexible DABCO-CH3CN array shows dielectric relaxation.

Ferroelectricity and antiferromagnetism in organic–inorganic hybrid (1,4-bis(imidazol-1-ylmethyl)benzene)CuCl4·H2O

A new [CuCl₄]²⁻ based organic–inorganic hybrid, (bix)CuCl₄·H₂O (bix = 1,4-bis(imidazol-1-ylmethyl)benzene), is synthesized via simple solution method, which shows the coexistence of ferroelectric and antiferromagnetic ordering in (bix)CuCl₄·H₂O.

Hierarchical Frameworks of Metal-Organic Cages with Axial Ferroelectric Anisotropy

Designing molecular crystals with switchable dipoles for ferroelectric applications is challenging and often serendipitous. Herein, we show a systematic approach toward hierarchical 1D, 2D and 3D frameworks that are assembled through successive linkage of metal-organic cages [Cu₆ (H₂ O)₁₂ (TPTA)₈ ]¹²⁺ with chloride ions. Their ferroelectric properties are due to the displacement of channel-bound nitrate counterions and solvated water molecules relative to the framework of cages. Ferroelectric measurements of crystals of discrete and 1D-framework assemblies showed axial ferroelectric anisotropy with high remnant polarisation. Both, the reversible formation of cage-connected networks and the observation of ferroelectric anisotropic behaviour are rare among metal-ligand cage assemblies.

A homochiral Zn–Dy heterometallic left-handed helical chain complex without chiral ligands: anion-induced assembly and multifunctional integration

The Zn₃Dy₂ pentanuclear complex evolved into a heterometallic left-handed helical chain multifunctional complex by the template action of perchlorate anion.

A novel co-crystallization molecular ferroelectric induced by the ordering of sulphate anions and hydrogen atoms

The co-crystallization complex [EG]·[Cu(phen)₂·SO₄] undergoes a paraelectric–ferroelectric phase transition around 272 K which was confirmed by the observation of a large dielectric anomaly.

Probing nanoscale functionalities of metal-organic framework nanocrystals

Experimental investigation of functional properties of metal-organic frameworks (MOFs) at nanoscale precision is challenging and rarely reported. In this study, we report the piezo- and ferroelectric properties of NUS-6 MOF nanocrystals using dual AC resonance tracking piezoresponse force microscopy and piezoresponse force spectroscopy for the first time. Both NUS-6-(Hf) and NUS-6-(Zr) nanocrystals displayed anomalous piezoelectricity with the calculated piezoelectric coefficient d_zz constants of 2.0-3.5 pm V^-1 and 1.5-2.5 pm V^-1, respectively. Moreover, NUS-6-(Hf) showed much better polarization-switching behaviors (ferroelectricity) than NUS-6-(Zr), featured by very low coercive biases in the ferroelectric hysteresis (PR) loop. Furthermore, elasticity and thermal stability of the NUS-6 nanocrystals have been presented. The results have opened a realm of probing piezo- and ferro-electric properties as well as mechanical properties of MOF nanocrystals, which are promising materials for applications in integrated microelectromechanical systems (MEMS).

Bistable N–H⋯N hydrogen bonds for reversibly modulating the dynamic motion in an organic co-crystal

Bistable N–H⋯N hydrogen bonds enable the modulation of the dynamic molecular motion by slowing down the fast rotation in 1,2-diazabicyclo(2.2.2)octane bis(thiourea).

Synthesis and characterization of CsSrCO3F – a beryllium-free new deep-ultraviolet nonlinear optical material

A noncentrosymmetric fluoride carbonate CsSrCO₃F has been synthesized which is a promising beryllium-free deep-UV nonlinear optical material.

Two different one-dimensional Cd(II) halide coordination polymers constructed through bridging carboxylate ligands

Two cadmium halide complexes, catena-poly[[chloridocadmium(II)]-di-μ-chlorido-[chloridocadmium(II)]-bis[μ2-4-(dimethylamino)pyridin-1-ium-1-acetate]-κ(3)O:O,O';κ(3)O,O':O], [CdCl2(C9H12N2O2)]n, (I), and catena-poly[1-cyanomethyl-1,4-diazoniabicyclo[2.2.2]octane [[dichloridocadmium(II)]-μ-oxalato-κ(4)O(1),O(2):O(1'),O(2')] monohydrate], {(C8H15N3)[CdCl2(C2O4)]·H2O}n, (II), were synthesized in aqueous solution. In (I), the Cd(II) cation is octahedrally coordinated by three O atoms from two carboxylate groups and by one terminal and two bridging chloride ligands. Neighbouring Cd(II) cations are linked together by chloride anions and bridging O atoms to form a one-dimensional zigzag chain. Hydrogen-bond interactions are involved in the formation of the two-dimensional network. In (II), each Cd(II) cation is octahedrally coordinated by four O atoms from two oxalic acid ligands and two terminal Cl(-) ligands. Neighbouring Cd(II) cations are linked together by oxalate groups to form a one-dimensional anionic chain, and the water molecules and organic cations are connected to this one-dimensional zigzag chain through hydrogen-bond interactions.

Two different anionic manganese(II) coordination polymers constructed through dicyanamide coordination bridges

In order to explore new metal coordination polymers and to search for new types of ferroelectrics among hybrid coordination polymers, two manganese dicyanamide complexes, poly[tetramethylammonium [di-μ3-dicyanamido-κ6N1:N3:N5-tri-μ2-dicyanamido-κ6N1:N5-dimanganese(II)]], {[(CH3)4N][Mn2(NCNCN)5]}n, (I), andcatena-poly[bis(butyltriphenylphosphonium) [[(dicyanamido-κN1)manganese(II)]-di-μ2-dicyanamido-κ4N1:N5]], {[(C4H9)(C6H5)3P]2[Mn(NCNCN)4]}n, (II), were synthesized in aqueous solution. In (I), one MnIIcation is octahedrally coordinated by six nitrile N atoms from six anionic dicyanamide (dca) ligands, while the second MnIIcation is coordinated by four nitrile N atoms and two amide N atoms from six anionic dca ligands. Neighbouring MnIIcations are linked together by μ-1,5- and μ-1,3,5-bridging dca anions to form a three-dimensional polymeric structure. The anionic framework exhibits a solvent-accessible void of 289.8 Å3, amounting to 28.0% of the total unit-cell volume. Each of the cavities in the network is occupied by only one tetramethylammonium cation. In (II), each MnIIcation is octahedrally coordinated by six nitrile N atoms from six dca ligands. Neighbouring MnIIcations are linked together by double dca bridges to form a one-dimensional polymeric chain, and C—H...N hydrogen-bonding interactions are involved in the formation of the one-dimensional layer structure.

A two-dimensional anionic CdII polymer constructed through dicyanamide coordination bridges

In the search for potential ferroelectric materials, molecular-based one-, two- and three-dimensional cadmium(II) organic-inorganic compounds have been of interest as they often display solid-solid phase transitions induced by a variation in temperature. A new cadmium dicyanamide complex, poly[4-dimethylamino-1-ethylpyridin-1-ium [tri-μ-dicyanamido-κ(6)N(1):N(5)-cadmium(II)]], {(C9H15N2)[Cd(C2N3)3]}n, was synthesized by the reaction of 4-dimethylamino-1-ethylpyridin-1-ium bromide, cadmium nitrate tetrahydrate and sodium dicyanamide in aqueous solution. In the crystal structure, each Cd(II) cation is octahedrally coordinated by six terminal N atoms from six anionic dicyanamide (dca) ligands. Neighbouring Cd(II) cations are linked together by dicyanamide bridges to form a two-dimensional coordination polymer. The organic cations are not involved in the formation of the supramolecular network.

ACdCO3F (A = K and Rb): new noncentrosymmetric materials with remarkably strong second-harmonic generation (SHG) responses enhanced via π-interaction

The remarkably large SHG efficiency of KCdCO₃F originates from enhancement via interatomic interactions between the s and p states of Cd²⁺ and the π-conjugated groups of the [CO₃]²⁻ unit.

A series of coordination polymers based on varied polycarboxylates and different imidazole-containing ligands: syntheses, crystal structures and physical properties

To investigate the effect of organic ligands on the coordination frameworks, seven nickel(ii) coordination polymers, based on varied polycarboxylates and different imidazole-containing ligands, are synthesized under hydrothermal method.

Series of lead oxide hydroxide nitrates obtained by adjusting the pH values of the reaction systems

A series of lead(II) nitrates have been synthesized by a hydrothermal method and adjusting the pH values of the reaction systems. Pb20O6(OH)16(NO3)12 and Pb2O(OH)NO3, crystallize in the centrosymmetric space group P1̅ and Pbca, respectively. The structure of Pb20O6(OH)16(NO3)12 features infinite cationic chains of [Pb20O6(OH)16]∞ running along c axis, and the nitrate groups as the counterions reside between adjacent chains, while the structure of Pb2O(OH)NO3 can be described as alternate stacking of cationic [Pb2O(OH)]∞ layers with anionic [NO3](-) layers along [001] direction by the weak Pb-O bonds, forming a 3D framework with 1D tunnels of 12-member rings (MRs). [Pb4(OH)4](NO3)4, crystallizing in the noncentrosymmetric space group Cc, has been studied as the nonlinear optical material for the first time. The second harmonic generation (SHG) measurement indicates that the SHG responses of [Pb4(OH)4](NO3)4 are 0.7 times that of KDP. Theoretical calculations confirmed the SHG efficiency of [Pb4(OH)4](NO3)4 originates from the cooperative effect of NO3(-) groups and lead oxygen polyhedras in the structure. Meanwhile, the relationship between pH value and ratio of Pb/OH(-) in the molecules presents a positive correlation, which results in the diversity of these structures under different pH value.

Two novel trimethylsulfonium salts with polymeric {[SbCl4]-}n or {[CdCl3]-}n anions

The title organic-inorganic hybrid salts poly[trimethylsulfonium [[dichloridoantimony(III)]-di-μ-chlorido]], {(C3H9S)[SbCl4]}n, (I), and catena-poly[trimethylsulfonium [cadmium(II)-tri-μ-chlorido]], {(C3H9S)[CdCl3]}n, (II), consist of trimethylsulfonium cations and polymeric {[SbCl4](-)}n or {[CdCl3](-)}n anions. The central metal atoms are coordinated by six Cl atoms, forming an anionic {[SbCl4](-)}n three-dimensional framework (two of the four bridging chloride anions are located on two different centres of inversion) or anionic {[CdCl3](-)}n one-dimensional chains. The trimethylsulfonium cation of (II) is disordered over two sets of sites in a 0.791 (4):0.209 (4) ratio. All the anions are linked by trimethylsulfonium cations through weak C-H···Cl hydrogen bonds to form three-dimensional structures.

Synthesis and characterization of Cd4YbO(BO3)3 – a congruent melting cadmium–ytterbium oxyborate with large nonlinear optical properties

A novel ultraviolet nonlinear-optical material Cd₄YbO(BO₃)₃ has been discovered in the CdO–Yb₂O₃–B₂O₃ system.

Molecular ferroelectrics: where electronics meet biology

In the last several years, we have witnessed significant advances in molecular ferroelectrics, with the ferroelectric properties of molecular crystals approaching those of barium titanate. In addition, ferroelectricity has been observed in biological systems, filling an important missing link in bioelectric phenomena. In this perspective, we will present short historical notes on ferroelectrics, followed by an overview of the fundamentals of ferroelectricity. The latest developments in molecular ferroelectrics and biological ferroelectricity will then be highlighted, and their implications and potential applications will be discussed. We close by noting molecular ferroelectric as an exciting frontier between electronics and biology, and a number of challenges ahead are also described.

A novel pentacoordinated cadmium compound: catena-poly[benzyltriethylammonium [[chloridocadmate(II)]-di-μ-chlorido]]

The structure of the title one-dimensional ABX3-type organic-inorganic hybrid complex, {(C13H22N)[CdCl3]}n, consists of benzyltriethylammonium cations and one-dimensional anionic {[CdCl3](-)}n chains, in which the Cd(II) centres are in an unusual two-layer five-coordinated arrangement. The Cd(II) atom is pentacoordinated by four bridging and one terminal chloride ligand, forming a slightly distorted trigonal bipyramidal ClCd(μ-Cl)4 arrangement. The trigonal bipyramid is linked by two opposite shared faces, giving rise to a zigzag linear anionic {[CdCl3](-)}n chain. The benzyltriethylammonium cations are located in the inter-space of the inorganic network. There are C-H···Cl hydrogen bonds present and these play a crucial role in linking the organic cations and inorganic layers, and also help assemble the components into a three-dimensional network.

A one-dimensional ABX3-type coordination polymer: catena-poly[benzyltrimethylammonium [tri-μ-chlorido-cadmium(II)]]

The crystal structure of the title novel one-dimensional ABX3-type organic-inorganic hybrid complex {(C10H16N)[CdCl3]}n, (I), consists of benzyltrimethylammonium (Me3BzN(+)) cations and one-dimensional anionic {[Cd(μ-Cl)3](-)}∞ chains. Each Cd(II) centre is hexacoordinated by bridging chloride ligands, giving a slightly distorted octahedral Cd(μ-Cl)6 arrangement. The octahedra are linked by two opposite shared faces, giving rise to an almost perfectly linear anionic {[Cd(μ-Cl)3](-)}∞ chain in the a-axis direction. Me3BzN(+) cations located in the inter-chain spaces balance the charge. Noncovalent static attracting forces (Coulombic and van der Waals forces) and nonclassical C-H···Cl hydrogen-bond interactions stabilize the crystal structure.

A potential molecular ferroelectric material: poly[[bis(1-aza-4-azoniabicyclo[2.2.2]octane)di-μ3-chlorido-tetra-μ2-chlorido-dichloridotricadmium(II)] dihydrate]

The title compound, {[Cd3(C6H13N2)2Cl8]·2H2O}n, consists of pendant protonated cationic diamine ligands bonded to an anionic one-dimensional coordination polymer chloridocadmate scaffold. Each coordination chain features two kinds of Cd(II) centre, each with distorted octahedral coordination geometry. One Cd(II) cation lies on a centre of inversion and is coordinated by six bridging chloride ligands, while the other is coordinated by four bridging chloride ligands, one terminal chloride ligand and a 1-aza-4-azoniabicyclo[2.2.2]octane aza N atom. This gives a reversible corner-sharing half-cubic linear polymer that lies along the crystallographic a direction. The chains interact through hydrogen bonding with solvent water, with each water molecule accepting one N-H...O interaction from a cation and donating to two O-H...Cl interactions with anionic chains, thus linking three separate chains and completing the packing structure.

Poly[bis(4-chloropyridinium) tetra-μ2-chlorido-tetrachloridotrimercurate(II)]

The structure of the title compound, {(C(5)H(5)ClN)(2)[Hg(3)Cl(8)]}(n), consists of 4-chloropyridinium cations and one-dimensional [Hg(3)Cl(8)](2-) anion chains. There are two coordination environments for Hg(II) in the inorganic chain. The first is a distorted tetrahedral geometry made up of an HgCl(2) unit with two Cl(-) anion bridges, while the second is an octahedral coordination geometry consisting of an HgCl(2) unit and four chloride-anion bridges. This gives rise to a novel three-layer centrosymmetric polymer. Finally, the three-dimensional network comes about through the many C-H···Cl and N-H···Cl hydrogen bonds that link the organic and inorganic layers.