Sui-Jun Liu

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.

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.

Emissive mononuclear Eu(III) and Tb(III) complexes bearing deprotonated 2,2′-bipyridyl-1,2,4-triazole terdentate ligands

Abstract A series of new emissive mononuclear Ln(III) complexes with deprotonated 2,2ʹ-bipyridyl-1,2,4-triazole terdentate ligands, [Ln(L)(DMF)2(NO3)2]∙n(solvent) (Ln = Eu (1 and 2), Tb (3 and 4), HL = 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-2,2′-bipyridine, 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine), have been synthesized and characterized. As revealed by X-ray crystallography, each Ln(III) has a distorted tricapped trigonal prism generated by three nitrogens from one 2,2ʹ-bipyridyl-1,2,4-triazolate chelate and six oxygens from two DMF molecules and two chelating nitrates, where 2,2ʹ-bipyridyl-1,2,4-triazole serves as a mono-anionic tridentate chelate via deprotonation of the 1,2,4-triazolyl-NH. Complexes 1–4 are all emissive at room temperature in solution and solid states, and the introduction of two methyl groups into the 2,2ʹ-bipyridyl ring is efficient in enhancing luminescence efficiencies of Ln(III) complexes.

Diversified magnetic behaviors of new nickel(II) and copper(II) azido coordination polymers templated by diethyl or triethyl amines

The reactions of NiII or CuII ions with N3− anions in the presence of templated diethyl or triethyl amines afford three new azido-bridged coordination polymers, namely, [Ni(N3)2(Deeda)] (1), (DeaH)[Cu3(N3)7] (2), and (TeaH)[Cu4(N3)9] (3), where Deeda, (DeaH)+ and (TeaH)+ represent N,N-diethylethane-1,2-diamine, diethylammonium and triethylammonium, respectively. Magnetic studies revealed that they exhibit metamagnetism, spin glass and canted ferromagnetism, respectively, induced by different coordination modes of the azide ligands.

First observation of mutual energy transfer of Mn4+–Er3+via different excitation in Gd2ZnTiO6:Mn4+/Er3+ phosphors

Mutual energy transfer between rare earth ions and transition metal ions in a single luminescence material easily achieves multifunctions by altering the excitation wavelength. In this study, we first observe the mutual energy transfer process between Mn4+ and Er3+via different excitations in Mn4+–Er3+ co-doped Gd2ZnTiO6 phosphors synthesized by a high temperature solid-state reaction. During the downshift energy transfer from Mn4+ to Er3+, the Gd2ZnTiO6:Mn4+/Er3+ phosphor exhibits a strong near-infrared emission around 1529 nm with a wide excitation band extending from 250 to 550 nm. Based on Dexters theory, the energy transfer mechanism mainly contributes to a dipole–dipole interaction between Mn4+ and Er3+ ions, which is responsible for the greatly enhanced emission at 1529 nm. Upon the upconversion energy transfer from Er3+ to Mn4+, the Gd2ZnTiO6:Mn4+/Er3+ phosphor shows a deep red emission of Mn4+ under 980 nm laser excitation. The energy transfer process from Er3+ to Mn4+ is fully demonstrated by variations in excitation power as well as luminescence lifetimes of 551 nm emission of Er3+. Two-photon processes and resonance energy transfer from Er3+ to Mn4+ are required to populate the 2E emitting level of Mn4+.

Structural phase transitions, dielectric bistability and luminescence of two bulky ion-pair crystals [N(C3H7)4]2[Ln(NO3)5] (Ln = Tb, Dy)

Two bulky ion-pair crystals [N(C3H7)4]2[Ln(NO3)5] (Ln = Tb or Dy) are synthesized and structurally characterized. Both compounds exhibit a dielectric bistable behaviour accompanied by a reversible structural phase transition above room temperature. In addition, the relatively rigid coordination configuration around the lanthanide ions makes the two ion-pair compounds function as promising green and yellow phosphors, respectively. The synthetic approach may be applicable to construct other multifunctional materials with dielectric bistability and luminescence based on large organic ammonium and lanthanide complex anions.

Homochiral luminescent lanthanide dinuclear complexes derived from a chiral carboxylate

A new family of homochiral lanthanide dinuclear complexes based on a chiral carboxylate, namely [Ln(R-pba)(3)(phen)](2) (Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9) and Ho (10), R-pba = (R)-2-phenylbutyric acid, phen = 1,10-phenanthroline), have been synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analyses and IR spectra. Complexes 1-10 are isostructural and crystallize in the chiral space group P2(1). Their optical activity and enantiomeric nature were confirmed by the circular dichroism spectra. Complexes 6, 8 and 9 exhibit strong fluorescent emissions with typical narrow emission bands of lanthanide ions and 6 and 8 display relatively high quantum yields. Magnetic investigations revealed that the weak antiferromagnetic exchange and/or the depopulation of the Ln(III) excited Stark sub-levels which exist in 7-10.

Large magnetic entropy changes in three GdIII coordination polymers containing GdIII chains

Three chain-based GdIII coordination polymers, namely [Gd2(SO4)3(phen)2(H2O)2]n (1), [Gd2(oda)2(ox)(H2O)6]n (2) and {[Gd2(glu)3(H2O)2]·4H2O}n (3) (phen = 1,10-phenanthroline, H2oda = oxydiacetic acid, H2ox = oxalic acid and H2glu = glutaric acid), have been successfully constructed by using multidentate O ligands under hydro/solvothermal conditions. Complex 1 has a one-dimensional (1D) chain bridged by inorganic sulfate, and complex 2 exhibits a 1D double-chain ladder-shaped structure connected by oxalate. While, complex 3 is a three-dimensional (3D) metal–organic framework composed of 1D chains. All of them display good thermal stabilities and large magnetic entropy changes with −ΔSmaxm > 31 J kg−1 K−1 (7 T), suggesting them to be good candidates for use as cryogenic magnetic refrigerants.