Songping D. Huang

Supramolecular bola-like ferroelectric: 4-methoxyanilinium tetrafluoroborate-18-crown-6.

Molecular motion is one of the structural foundations for the development of functional molecular materials such as artificial motors and molecular ferroelectrics. Herein, we show that pendulum-like motion of the terminal group of a molecule causes a ferroelectric phase transition. Complex 4-methoxyanilinium tetrafluoroborate-18-crown-6 ([C(7)H(10)NO(18-crown-6)](+)[BF(4)](-), 1) shows a second-order ferroelectric phase transition at 127 K, together with an abrupt dielectric anomaly, Debye-type relaxation behavior, and the symmetry breaking confirmed by temperature dependence of second harmonic generation effect. The origin of the polarization is due to the order-disorder transition of the pendulum-like motions of the terminal para-methyl group of the 4-methoxyanilinium guest cation; that is, the freezing of pendulum motion at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. The supramolecular bola-like ferroelectric is distinct from the precedent ferroelectrics and will open a new avenue for the design of polar functional materials.

Hydrogen-Bonded Ferroelectrics Based on Metal−Organic Coordination

Metal-organic coordination (MOC)-type ferroelectrics, cobalt(II) (R)-2-methylpiperazine (MPPA) trichloride [Co(II)Cl(3)(H-MPPA)], was constructed through hydrogen bonds. It is a good ferroelectric candidate with a P(s) = 6.8 microC.cm(-2) as high as almost twice that of triglycine sulfate (P(s) = 3.5 microC.cm(-2)) and significantly larger than that of KH(2)PO(4) at the low-temperature ferroelectric phase Fdd2. [Co(II)Cl(3)(H-MPPA)] is the first example of ferroelectric MOC that can really reach the spontaneous polarization status and opens up a new avenue to explore novel MOC-based ferroelectrics.

Discovery of New Ferroelectrics: [H2dbco]2·[Cl3]·[CuCl3(H2O)2]·H2O (dbco = 1,4-Diaza-bicyclo[2.2.2]octane)

Compound [H(2)dbco](2) x [Cl(3)] x [CuCl(3)(H(2)O)(2)] x H(2)O undergoes a sharp dielectric anomaly and a paraelectric-to-ferroelectric phase transition at approximately -23 degrees C with a spontaneous polarization of 1.04 microC cm(-2), being the first molecular metal coordination compound ferroelectrics with a large dielectric response involving a 2 orders of magnitude enhancement and distinct Curie phase transition point. This work has proved an effective way for exploration of new ferroelectrics based on a five-coordinated divalent metal through the combination of crystal engineering and Landau phase transition theory.

A lead-halide perovskite molecular ferroelectric semiconductor

Inorganic semiconductor ferroelectrics such as BiFeO3 have shown great potential in photovoltaic and other applications. Currently, semiconducting properties and the corresponding application in optoelectronic devices of hybrid organo-plumbate or stannate are a hot topic of academic research; more and more of such hybrids have been synthesized. Structurally, these hybrids are suitable for exploration of ferroelectricity. Therefore, the design of molecular ferroelectric semiconductors based on these hybrids provides a possibility to obtain new or high-performance semiconductor ferroelectrics. Here we investigated Pb-layered perovskites, and found the layer perovskite (benzylammonium)2PbCl4 is ferroelectric with semiconducting behaviours. It has a larger ferroelectric spontaneous polarization Ps=13 μC cm−2 and a higher Curie temperature Tc=438 K with a band gap of 3.65 eV. This finding throws light on the new properties of the hybrid organo-plumbate or stannate compounds and provides a new way to develop new semiconductor ferroelectrics.

3D Framework Containing Cu4Br4 Cubane as Connecting Node with Strong Ferroelectricity

The methanolothermal reaction of (S)-1,4-diallyl-2-methylpiperazine (DAMP) with an excess CuBr affords a novel homochiral 3D framework (DAMP)3(Cu4Br4)2(H2O)3 (1) in which Cu4Br4 cubane acts as a connecting node to mimic the pure inorganic role in the ferroelectricity to enhance the remnant polarization value which is comparable to that of BaTiO3 synthesized by peptide-assisted synthesis.

New Ferroelectrics Based on Divalent Metal Ion Alum

A detailed study of two alum-type complexes containing the SeO(4)(2-) anion, 1,4-diazoniabicyclo[2.2.2]octane hexaaquacopper(II) bis(selenate) [(H(2)dbco)Cu(H(2)O)(6)(SeO(4))(2), 1] and its deuterated analogue (D(2)dbco)Cu(D(2)O)(6)(SeO(4))(2) (2), has revealed that 1 and 2 are new ferroelectrics that undergo a paraelectric-ferroelectric phase transition at ca. -140 to -138 degrees C as a result of order-disorder features of the cation ([H(2)dbco](2+) or [D(2)dbco](2+)) and anion (selenate). These are the first examples of ferroelectrics based on divalent metal anion alum analogues since the discovery of ferroelectrics based on trivalent metal anion alum in approximately 1960.

Ferroelectricity Induced by Ordering of Twisting Motion in a Molecular Rotor

A novel mononuclear metal-organic compound, [Cu(Hdabco)(H(2)O)Cl(3)] (1, dabco = 1,4-diazabicyclo[2.2.2]octane) in which the Cu(II) cation adopts a slightly distorted bipyramidal geometry where the three Cl anions constitute the equatorial plane and the Hdabco cation and H(2)O molecule occupy the two axial positions, was synthesized. Its paraelectric-to-ferroelectric phase transition at 235 K (T(c)) and dynamic behaviors were characterized by single crystal X-ray diffraction analysis, thermal analysis, dielectric and ferroelectric measurements, second harmonic generation experiments, and solid-state nuclear magnetic resonance measurements. Compound 1 behaves as a molecular rotor above room temperature in which the (Hdabco) part rotates around the N···N axis as a rotator and the [Cu(H(2)O)Cl(3)] part acts as a stator. In the temperature range 235-301 K, a twisting motion of the rotator is confirmed. Below the T(c), the motions of the rotor are frozen and the molecules become ordered, corresponding to a ferroelectric phase. Origin of the ferroelectricity was ascribed to relative movements of the anions and cations from the equilibrium position, which is induced by the order-disorder transformation of the twisting motion of the molecule between the ferroelectric and paraelectric phases. Study of the deuterated analogue [Cu(Ddabco)(D(2)O)Cl(3)] (2) excludes the possibility of proton ordering as the origin of the ferroelectricity in 1.

Dual purpose Prussian blue nanoparticles for cellular imaging and drug delivery: a new generation of T1-weighted MRI contrast and small molecule delivery agents

A simple and improved aqueous synthetic procedure using flash heating for preparing biocompatible Prussian blue nanoparticles (PBNPs) with the single-crystal-like feature was developed. This method entailed the use of citric acid as a chelator to complex ferric ions in the precursor and as an in situ capping agent to prevent the PB nanoparticles formed in solution from aggregation. The citrate-coated PBNPs, which can be surface functionalized with small molecules, were readily internalized by cells and exhibited no detectable cytotoxicity. Furthermore, such nanoparticles do not trigger the production of reactive oxygen species (ROS) in cells via the Fenton reaction. The potential of using such PBNPs as an effective T1-weighted cellular MRI contrast agent has also been demonstrated. These properties suggest that PBNPs are an attractive dual purpose nanoplatform for developing the next generation of nanoparticle-based T1-weighted MRI contrast agents as well as delivery vehicles for small molecules.

Cysteine-assisted tailoring of adsorption properties and particle size of polymer and carbon spheres.

A series of cysteine-stabilized phenolic resin-based polymer and carbon spheres were prepared by the modified Stöber method. Cysteine plays a very important role in the proposed one-pot synthesis of the aforementioned spheres; namely, it acts as a particle stabilizer and a source of heteroatoms (nitrogen and sulfur) that can be introduced into these spheres. The diameter of these spheres can be tuned in the range of 70-610 nm by adjusting the cysteine amount and reaction temperature. Since polymer spheres obtained in the presence of cysteine contain sulfur and nitrogen heteroatoms, they were tested for adsorption of copper ions. It is shown that adsorption isotherms recorded for copper ions can be well fitted by Langmuir equation, giving unprecedented adsorption capacities up to ~65 mg/g.

Adsorption of Lead Ions from Aqueous Phase on Mesoporous Silica with P-Containing Pendant Groups

Mesoporous silica materials with hydroxyphosphatoethyl pendant groups (POH-MS) were obtained by a two-step process: (1) block copolymer Pluronic P123-templated synthesis of mesoporous silica with diethylphosphatoethyl groups (DP-MS) by co-condensation of diethylphosphatoethyl triethoxysilane (DPTS) and tetraethylorthosilicate (TEOS) under acidic conditions and (2) conversion of diethylphosphatoethyl into hydroxyphosphatoethyl groups upon suitable treatment with concentrated hydrochloric acid. The DP-MS samples obtained by using up to 20% of DPTS featured hexagonally ordered mesopores, narrow pore size distribution and high specific surface area. Conversion of DP-MS to mesoporous silica with hydroxyphosphatoethyl groups (POH-MS) resulted in the enlargement of the specific surface area, total porosity, and microporosity. High affinity of hydroxyphosphatoethyl groups toward lead ions (Pb(2+)) makes the POH-MS materials attractive sorbents for lead ions, which is reflected by high lead uptake reaching 272 mg of Pb(2+) per gram of POH-MS. This study shows that the simple and effective co-condensation strategy assures high loading of P-containing groups showing high affinity toward lead ions, which is of great importance for removal of highly toxic lead ions from contaminated water.