Yu-Hui Tan

In situ synthesis and ferroelectric, SHG response, and luminescent properties of a novel 3D acentric zinc coordination polymer.

The 3D acentric metal-organic framework (MOF) of [Zn(Mitz)Cl](n) [1; Mitz = 3-tetrazolyl-6-methyl-5-(4-pyridyl)-2-pyridone] was obtained from in situ [2 + 3] cycloaddition reactions of milrinone [=3-cyano-6-methyl-5-(4-pyridyl)-2-pyridone] with sodium azide in the presence of ZnCl(2) as the Lewis acid. The compound is a typical ferroelectric material with an electric hysteresis loop showing a remnant polarization (P(r)) of ca. 0.21 μC/cm(2) and a coercive field (E(c)) of 2600 V/cm. Powdered samples of 1 display strong second-harmonic-generation responses of ∼2 times larger than that of KH(2)PO(4). Photoluminescent study show that complex 1 and the milrinone ligand exhibit maximal emission peaks at around 409 and 401 nm, respectively, in the solid state at room temperature.

Unusual High-Temperature Reversible Phase-Transition Behavior, Structures, and Dielectric-Ferroelectric Properties of Two New Crown Ether Clathrates.

Molecular ferroelectrics with high-temperature reversible phase-transition behaviors are very rare and have currently become one of the hotspots in the field of ferroelectric materials. Herein we display two new crown ether clathrates possessing unusual high-temperature ferroelectric phase-transition behaviors, cyclohexyl ammonium 18-crown-6 tetrafluoroborate (or perchlorate), [Hcha-(18-crown-6)](+) [BF4](-) (1) and [Hcha-(18-crown-6)](+)[ClO4](-) (2) (Hcha = protonated cyclohexyl ammonium). We have proven their reversible structural phase transitions by variable-temperature PXRD measurements and temperature evolutions of Raman bands. Both clathrates exhibit clear ferroelectric phase transitions at about 397 and 390 K, respectively, revealed by the thermal anomalies of differential scanning calorimetry (DSC) measurements, together with abrupt dielectric anomalies in the heating and cooling processes. The measurements on ferroelectric properties using the single crystals showed optimized spontaneous polarization (Ps) of ca. 3.27 μC cm(-2) for 1 and 3.78 μC cm(-2) for 2.

Spontaneous Resolution, Asymmetric Catalysis, and Fluorescence Properties of Δ- and Λ-[Cu(Tzmp)]n Enantiomers from in Situ [2 + 3] Cycloaddition Synthesis

Although a number of acentric or chiral tetrazole complexes were synthesized from Sharpless reaction, there are no spontaneous resolution Cu(I)-tetrazole compounds from in situ [2 + 3] cycloaddition synthesis that have been reported before. The first enantiomers Δ- and Λ- of metal tetrazole compound [Cu(Tzmp)]n (1) (HTzmp = 3-tetrazolemethylpyridine) were obtained and isolated from in situ [2 + 3] cycloaddition reactions of a flexible organic nitrile (3-cyanomethylpyridine) with sodium azide in the presence of CuCl2 as the Lewis acid. Δ-1 and Λ-1 feature a homochiral helical coordination polymeric system and {4(4).6(2)} two-dimensional framework. The photoluminescence study suggests 1 exhibits strong green fluorescence in solid state with maximal emission peaks around 535 nm. Remarkably, the Δ- and Λ- of [Cu(Tzmp)]n (1) catalyzes the enantioselective Henry reaction with high yield (more than 96%) and certain enantioselectivity (up to 69%).

Solvothermal synthesis, structure, and fluorescence properties of three d10 polymers assembled from semi-rigid V-shaped aza-bridged multicarboxylate

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand, 2,2′-azanediyldibenzoic acid (H2L), and M(OH)2 (M = Cd, Zn) in the presence of different N-donor ancillary ligands, 4,4′-bipyridine (bpy) and pyridine (py), afford three novel coordination polymers: [Cd2(L)2(bpy)1.5(H2O)]n (1), [Cd2(L)(Py)2]n (2), and [Zn2(L)2]n (3). These polymers show great differences in regard to their structures and properties due to the variation in the ancillary ligands and in the coordination geometry of the metal ions. Compound 1 exhibits a 3D supramolecular network assembled from 2D layered architecture composed of dinucelar cadmium subunits via intermolecular π⋯π and C–H⋯π interactions. The supramolecular structure of compound 2 is built from the packing of two homochiral helical chain. Compound 3 possesses two crystallographically nonequivalent metal atoms with Zn1 in a four-coordinated tetrahedron geometry and Zn2 in a five-coordinated trigonal bipyramid geometry. Five different coordination modes, ranging from μ2, μ3 and μ4, have been observed in the H2L ligands. The solid-state fluorescence spectra show that complexes 1 and 2 exhibit small shifts to the blue, while 3 is red shifted with respect to the free ligand.

Reversible structural phase transition, ferroelectric and switchable dielectric properties of an adduct molecule of hexamethylenetetramine ferrocene carboxylic acid

Metallo-organic molecules showing reversible structural phase transitions accompanied with ferroelectric and dielectric properties have seldom been reported. By making use of the “driving/controlling force” from the rotating motion of cyclopentadienyl rings for a reversible structural transition and then carrying out structural modifications on their local parts to create remnant polarization through this molecular system, we designed and constructed a new ferroelectric, which is the adduct of hexamethylenetetramine ferrocene carboxylic acid, (C6H12N4)[Fe(C5H5)(C6H5O2)] (1). Compound 1 undergoes a reversible structural phase transition at around 187 K, which is confirmed by remarkable dielectric and heat anomalies. The synergistic interactions of the twisting motions of the adduct molecules and the inner cyclopentadienyl rings lead to the reversible phase transition. A dipole moment from amine group to carboxylic acid at low temperature produces a net spontaneous polarization, which results in the ferroelectricity of 1-LTP. On further investigation, it is observed that compound 1 has a perfect ferroelectric hysteresis loop with a spontaneous polarization of 3.95 μC cm−2.

Reversible Phase Transition with Ultralarge Dielectric Relaxation Behaviors in Succinimide Lithium(I) Hybrids

Dielectric relaxations have widely applied on high permittivity capacitors, dielectric switches, ferroelectrics, pyroelectrics, and electrical insulating materials. However, few investigations of large dielectric relaxation behaviors on organic-inorganic hybrid materials have been documented before. Here we present a novel two-dimensional succinimide lithium(I) hybrid compound, [Li(PDD)2ClO4]n, 1, (PDD = 2,5-pyrrolidinedione = succinimide) which shows reversible phase transition behavior in the vicinity of 228 K accompanied by an unusual symmetry breaking from I41/amd to C2/c. X-ray single crystal diffractions analysis indicates the twist motion of pyrrolidine heterocycles, and order-disorder motion of ClO4- anions triggered the reversible phase transition. By means of an intuitive crystallographic model (rattling ion model), we further illustrated the mechanism of the interesting reversible phase transition. Particularly, 1 shows ultralarge dielectric relaxation behavior in the vicinity of the phase transition by its dielectric constant dependence on temperatures and frequencies as well as its Cole-Cole relation.

One pot synthesis, crystal structures and properties of two new MOFs with imidazole-containing tripodal ligand

Two new different Cu(II) MOFs with the same 1,3,5-tris(1-imidazolyl) benzene (tib) ligand {[Cu(tib)2]·(H2O)2·Br2}n (1) and {[Cu2(tib)·Br·Cl]·2Br}n (2) were obtained by one pot synthesized of tib with CuBr in the presences of HCl and water. X-ray single crystal diffraction analyses indicate that both complexes 1 and 2 have two dimensional frameworks containing different building blocks. Each Cu(II) atom in complex 1 is coordinated by four N atoms from different tib ligands. However, there are two different cryptographic Cu(II) atoms in complex 2, one is four coordinated by two bromine atoms and two N atoms from different tib ligands, the other is six coordinated by two chloride atoms and four N atoms from different tib ligands. The thermal gravimetric analysis of complexes 1 and 2 are depicted in the paper.