Chiral All-Nitrogen-Coordinated Dysprosium Single-Molecule Magnets.

Two pairs of chiral end-on azido-bridged dinuclear hexaazamacrocycles, [Dy2 (LN6 R/S )2 (N3 )2 Cl2 ](BPh4 )2 (1R/1S) and [Dy2 (LN6 R/S )2 (N3 )4 ]Cl2 (2R/2S) (LN6 R/S is hexaazamacrocyclic neutral Schiff base ligand derived from 2,6-diformylpyridine and (1R, 2R)/(1S, 2S)-diaminocyclohexane), were constructed by adjusting the molar ratio of sodium azide to Dy(III) macrocycle precursor. Structural analyses reveal that all Dy(III) centers in complexes 1R/1S and 2R/2S are nine-coordinate with hula-loop coordination geometry, and the differences between 1R/1S and 2R/2S are the terminal coordination anion and counter anion. Magnetic studies indicate that complex 2S displays typical SMM behaviors under a zero dc field, whereas 1S just shows slow relaxation of magnetization resulting from a relatively weak axial crystal field. Significantly, complex 2R/2S represents the first homochiral all-nitrogen-coordinated lanthanide single-molecule magnet.

Growth of SnX2 (X = Br, I) Single Crystals with Self-Trapped Exciton Emission.

Broadband emission with a large Stokes shift is important to obtain an excellent color rendering index of the solid-state lighting device. Among low-dimensional material and perovskite-like phosphors with broadband self-trapped emission, Sn-based phosphors have attracted much attention due to their high photoluminescence quantum yield (PLQY). However, the disadvantage is that the synthesis of Sn-based phosphors needs to be performed in a glovebox. Upon photoexcitation, the broadband emission of self-trapped excitons results from exciton-phonon coupling induced by the transient distortion of the lattice. Low-dimensional material structures often promote self-trapped emission because of more vibrational degrees of freedom and easier polarization under photoexcitation. Here, zero-dimensional (0D) SnX2 (X = Br, I) single crystals are synthesized by the solvent evaporation method in the air. SnX2 emits blue light, broadband yellow light, and deep red light, among which SnBr2 has the best luminescence performance. The photoluminescence quantum yield (PLQY) of SnBr2 reaches 85% and the Stokes shift reaches 265 nm. The PL intensity of SnX2 is linearly related to excitation power, which preliminarily indicates that the origin of SnX2 luminescence is attributed to self-trapped emission (STE). The white light-emitting diodes (WLEDs) were fabricated using yellow-emitting SnBr2 and blue-emitting BaMgAl10O17:Eu2+, which has a low correlated color temperature (3160 K) and a relatively common color rendering index (79).

Enhancing magnetic relaxation through subcomponent self-assembly from a Dy2 to Dy4 grid.

The subcomponent self-assembly of 4,6-dihydrazinopyrimidine and o-vanillin/salicylaldehyde with different DyIII salts leads to the formation of Dy2 (1-3) and grid-like Dy4 (4) compounds with formulas of [Dy2L(DMF)4(NO3)4]·2DMF (1), [Dy2L2(CH3COO)4(CH3OH)2]·10H2O (2), [Dy2L'2(CH3COO)4(CH3OH)2]·2H2O·2CH3OH (3) and [Dy4Na2L2(µ2-OH)2(PhCOO)8(CH3OH)(H2O)]·CH3CN·2CH3OH·7H2O (4). In all cases, the DyIII ions are nine coordinate but the different features of coordinated solvent molecules and anions result in diverse coordination geometries in their respective structures. Notably, by introducing various axial coordinating anions with different electronegativities (NO3-, CH3COO- and C6H5COO-), the effective energy barriers were progressively enhanced (52-207 K) in this system. Detailed magnetic studies for these complexes revealed obvious magnetic interactions in complex 1 and clear single molecule magnet (SMM) behavior with anisotropy barriers of 52, 56 and 58.4 K for 1-3, respectively. Moreover, we find that the incorporation of benzoates into the axial position of the DyIII ions in complex 4 leads to the occurrence of two clear distinct relaxation processes, with energy barriers of 94.9 and 207.2 K, respectively. This result presents an example of the effects of axial coordinating anions on the SMM behavior, providing a valid route towards enhancing the slow magnetic relaxation of 4f based SMMs via incorporating diverse coordination anions into the subcomponent self-assembly system.

Air-stable chiral double-decker Dy(III) macrocycles with fluoride ion as the sole axial ligand.

A pair of air-stable double-decker Dy(III) macrocyclic enantiomers featuring sole fluoride axial ligands were designed and structurally and magnetically characterized. They displayed strong intramolecular ferromagnetic coupling and two-step relaxation of magnetization supported by the collinear arrangement of the magnetic anisotropy axes and obviously different outer Dy-F distances for two Dy(III) ions, respectively.

Aggregation-Induced Emission and Single-Molecule Magnet Behavior of TPE-Based Ln(III) Complexes.

Multifunctional lanthanide complexes have been studied extensively owing to their promising applications in information storage, luminescence sensors and magneto-optical devices, etc. Here, we report the facile synthesis of two discrete highly thermally stable lanthanide compounds, Ln(hfac)3 (TPE-tz) (Ln=Eu, Dy), by the reaction of the AIE-active organic ligand with Ln(III) ß-diketonate precursor. Due to different energy gaps between the triplet state of the ligand and the accepted level of Ln(III) ions, Eu(hfac)3 (TPE-tz) exhibited remarkably enhanced luminescence intensity upon aggregation, i. e., a typical AIE behavior, while Dy(hfac)3 (TPE-tz) displayed weak characteristic emission bands of Dy(III) ions. In addition, Dy(hfac)3 (TPE-tz) showed field-induced SMM behavior. This work shows that careful choice of auxiliary ligands paves the way for the construction of multifunctional lanthanide smart materials.

Terminal-fluoride-coordinated air-stable chiral dysprosium single-molecule magnets.

Terminal fluoride ligands generate strong magnetic anisotropy in air-stable chiral dysprosium enantiomers supported by a bulky equatorial macrocycle, exhibiting a typical zero-field single-molecule magnet behaviour.

Fabrication of VO Nanorings on a Porous Carbon Architecture for High-Performance Li-Ion Batteries.

Vanadium monoxide (VO) is a promising candidate as an anode for lithium-ion batteries due to its high theoretical capacity, low cost, and considerable electronic conductivity. Unfortunately, a large volume change during electrochemical processes obstructs its practical application. In this work, a composite of VO nanorings grown on a porous carbon architecture is prepared via a topochemical self-reduction approach. When used as an anode for lithium-ion batteries, improved redox kinetics from enhanced electronic conduction and the corresponding fast lithium-ion diffusion is observed to greatly promote the electrochemical performance of lithium-ion batteries. The resulting composite delivered a reversible capacity of 336 mA h g-1 after 400 cycles at 10 A g-1 with a capacity retention of 85%, owing to the synergistic effect of VO nanorings and porous carbon in alleviating volume changes that result in a long-term cycling ability at a high current density. At 20 A g-1, the composite anode exhibited a rate capability of 235 mA h g-1, superior to all VO-based electrodes reported in the literature. Furthermore, a full cell was first fabricated by employing VO@C-2 as the anode and LiFePO4 as the cathode, which exhibited a capacity of 213 mA h g-1 after 100 cycles at 0.1 A g-1, indicating the potential of VO as an anode for practical application.

Coordination anion effects on the geometry and magnetic interaction of binuclear Dy2 single-molecule magnets.

Two new dimeric dysprosium(III) complexes, [Dy2(HL)2(SCN)2]·2CH3CN (1) and [Dy2(HL)2(NO3)2]·2CH3CN·2H2O (2), have been assembled using the H3L multidentate ligand (H3L = 2,2'-((((2-hydroxy-5-methyl-1,3-phenylene)bis(methylene))bis((pyridin-2-ylmethyl)azanediyl))bis(methylene))diphenol). The use of different coordination anions for the two complexes results in distinct coordination geometries of the metal sites. The Dy centers in complexes 1 and 2 display capped octahedron and triangular dodecahedron coordination geometries, respectively. Consequently, the two compounds exhibit distinct dc and ac magnetic properties. Complex 1 behaves as a single molecule magnet (SMM) while no SMM behavior is observed for complex 2. Although complexes 1 and 2 possess a similar core of Dy2O2, their different coordination anions lead to two distinct magnetic interactions, namely ferromagnetic and antiferromagnetic, respectively. Ab initio calculations reveal that these interactions may result from strong intramolecular dipolar couplings that are ferromagnetic for 1 but antiferromagnetic for 2, while exchange couplings are antiferromagnetic in both cases.