He-Rui Wen

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%).

Three-dimensional two-fold interpenetrated CrIII–GdIII heterometallic framework as an attractive cryogenic magnetorefrigerant

The hydrothermal reaction of CrO3, Gd2O3 and iminodiacetic acid (H2IDA) yields a three-dimensional (3D) two-fold interpenetrated complex [CrGd(IDA)2(C2O4)]∞ (1). The oxalate anions were generated in situ under hydrothermal conditions. Magnetic studies suggest the presence of weak antiferromagnetic coupling between CrIII and GdIII ions, and negligible GdIII⋯GdIII and CrIII⋯CrIII couplings. Complex 1 exhibits a large magnetocaloric effect with − ΔSmaxm = 39.86 J kg−1 K−1 (the mass aspect) and 93.69 mJ cm−3 K−1 (the volumetric aspect), making it an attractive refrigerant for low-temperature applications.

Two GdIII complexes derived from dicarboxylate ligands as cryogenic magnetorefrigerants

Two GdIII complexes, namely [Gd2(OH)2(oda)2(H2O)4]∞ (1) and {[Gd(fum)(ox)0.5(H2O)2]·2H2O}∞ (2) (H2oda = oxydiacetic acid, H2fum = fumaric acid and H2ox = oxalic acid), have been constructed via hydrothermal reactions. Complex 1 has a one-dimensional (1D) chain structure based on hydroxyl-bridged Gd2O2 cores, while complex 2 exhibits a three-dimensional (3D) framework consisting of Gd6 macrocycles, and can also be seen as a 3D layer-pillar structure with intersected channels occupied by guest water. Magnetic studies indicate that weak antiferromagnetic and ferromagnetic interactions exist between adjacent GdIII ions in 1 and 2, which display large magnetocaloric effects with −ΔSmaxm = 43.3 and 37.1 J kg−1 K−1 for ΔH = 7 T, respectively. Notably, the maximum entropy changes (−ΔSmaxm) of 1 and 2 reach 29.9 and 28.5 J kg−1 K−1, respectively, at 2 K for a moderate field change (ΔH = 3 T). Therefore, 1 and 2 could be regarded as potential magnetorefrigerants for low-temperature applications.

NaGd(WO4)2:Yb3+/Er3+ phosphors: hydrothermal synthesis, optical spectroscopy and green upconverted temperature sensing behavior

NaGd(WO4)2:Yb3+/Er3+ (NGW:Yb3+/Er3+) phosphors co-doped with Yb3+ (12–24 at%, at% i.e. atomic percent) and Er3+ ions (1–10 at%) were synthesized by a facile hydrothermal process. Under 980 nm excitation, NGW:Yb3+/Er3+ phosphors exhibited strong green upconversion (UC) emission bands centered at 532 nm (2H11/2 → 4I15/2) and 554 nm (4S3/2 → 4I15/2) and weak red emissions near 658 and 671 nm (4F9/2 → 4I15/2). The optimum doping concentrations of Er3+ and Yb3+ for the highest emission intensity were determined by using X-ray diffraction (XRD) and photoluminescence (PL) analyses. Concentration dependent studies revealed that the optimal composition was realized for the 20 at% Yb3+ and 6.0 at% Er3+-doping concentration with a strong green emission. A possible UC mechanism for NGW:Yb3+/Er3+ depends on the pump power is discussed. The temperature dependence of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaking at 532 and 554 nm was studied in the range of 293–573 K under excitation by a 980 diode laser and the maximum sensitivity was approximately 114.96 × 10−4 K−1 at 453 K. This indicates that NGW:Yb3+/Er3+ phosphors are potential candidates for optical temperature sensors with high sensitivity.

Two novel coordination polymers constructed from 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide ligands

Utilizing 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide (H2BDCD) and CuCl2·2H2O (or Ba(NO3)2·6H2O) under hydrothermal conditions produces two novel coordination polymers {[Cu(BDCD)]·EtOH}n, 1 and [Ba(BDCD)·2H2O]n, 2. X-ray structure determination reveals that compound 1 shows a two-dimensional structure which is constructed by a well known (4,8) three-connected bimodal net, compound 2 exhibits a novel three-dimensional structure with interesting barium pillars as building blocks.

Luminescent monometallic Cu(I) triphenylphosphine complexes based on methylated 5-trifluoromethyl-3-(2′-pyridyl)-1,2,4-triazole ligands

A new family of five new mononuclear Cu(I) triphenylphosphine complexes derived from methylated 5-trifluoromethyl-3-(2′-pyridyl)-1,2,4-triazole ligands has been synthesized and well characterized. They all show an N2P2 distorted tetrahedral geometry and the methylated 5-trifluoromethyl-3-(2′-pyridyl)-1,2,4-triazole ligands display the mono-anionic η2(N1,N2) and charge-neutral η2(N1,N4) chelating coordination modes, along with the 1,2,4-triazolyl ring inversion induced by the NH ↔ N− transformation. These Cu(I) complexes are all emissive in solution and solid states at ambient temperature, which can be well modulated by changing the methyl position on the pyridyl ring and regulating the NH ↔ N− conversion of the 1,2,4-triazolyl ring. It is also shown that the deprotonation of 1,2,4-triazolyl-NH can markedly improve the luminescence properties of Cu(I) complexes.

Luminescent triply-bridged dicopper(I) complex possessing 3,5-bis{6-(2,2′-dipyridyl)}pyrazole as a bis-chelating ligand

A new triply-bridged dicopper(I) complex, [Cu2(μ-dppm)2(μ-HL)](NO3)2 (1), has been prepared via successive treatment of cupric nitrate trihydrate with bis(diphenylphosphino)methane (dppm) and 3,5-bis{6-(2,2′-dipyridyl)}pyrazole (HL) in 2 : 4 : 1 molar ratio in dichloromethane. X-ray diffraction analysis of 1 reveals that the two Cu(I)s are in highly distorted tetrahedral environments with a distance of 4.2775(10) Å, triply bridged by two dppm ligands and one HL chelate as a bis-bidentate bridging ligand through two bipyridyl moieties. Intermolecular N···H–C hydrogen bonding and π···H–C interactions assemble the [Cu2(μ-dppm)2(μ-HL)]2+ cations into a 3-D supramolecular architecture with extended channels along the b-axis, filled with methanol and anions. Complex 1 shows weak low-energy absorptions at 350–425 nm, tentatively ascribed to Cu(I) to HL metal-to-ligand charge-transfer (MLCT) transition, probably mixed with some ILCT character inside HL. The emission is observed at ambient temperature for 1, both in solution and in the solid state, originating from the MLCT excited states.

Synthesis and characterization of emissive mononuclear Cu(I) complexes with 5-tert-butyl-3-(pyrimidine-2-yl)-1H-1,2, 4-triazole

A new series of mononuclear copper(I) halide complexes possessing 5-tert-butyl-3-(pyrimidine-2-yl)-1H-1,2,4-triazole (bpmtzH) and PPh3, Cu(bpmtzH)(PPh3)X (X = I (1); Br (2); Cl (3)), have been synthesized and characterized. As revealed via X-ray crystallography, 1–3 show a chiral, distorted tetrahedral N2PX arrangement, in which bpmtzH is a neutral bidentate chelating ligand using the 4-N of the 1,2,4-triazolyl ring and one N donor from the 2-pyrimidyl ring, consistent with the computational results. A comparatively weak low-energy absorption tail is observed between 320 and 450 nm for CH2Cl2 solutions of 1–3 at room temperature, ascribing to charge-transfer transitions with appreciable metal-to-ligand charge transfer (MLCT) character. Complexes 1–3 in the solid state have good luminescence at ambient temperature, although they are non-emissive in solution. The solid-state emission, most likely originating from both 3MLCT and 3XLCT transitions, can be modulated via alteration of the halide bound to {Cu(bpmtzH)(PPh3)} motif. Graphical Abstract