Slow magnetic relaxation and photoluminescence behaviors of dilanthanide complexes bearing N_(8)O_(2)donor macrocyclic ligand

On account of the complicated magnetic exchange interactions between lanthanide ions,binuclear lanthanide complexes have broad application prospect in the field of single-molecule magnets.Therefore,it is necessary to develop reasonable bridging ligands to manipulate the directional assembly of binuclear lanthanide complexes.Herein,we selected the macrocyclic ligand L^(N_(8)O_(2))to build up two new dilanthanide complexes[Ln_(2)(LN_(8)O_(2))(OpyO)_(2)(H_(2)O)2](NO_(3))_(2)(1-Ln,Ln=Dy,Tb;LN_(8)O_(2)=hexamethyl-tetraaza-dioxe-dipyrazolacycloicosaphane-2,9,12,19-tetraene;OpyOH=2-pyridinol-1-oxide).Dynamic magnetic studies show that 1-Dy exhibits slow relaxation behavior under a 1 kOe applied field.Further fitting analysis of relaxation times gives the effective energy barrier of 38.2 cm^(−1),and reveals that the slow magnetic relaxation behavior is dominated by the Orbach and Raman processes.High-resolution luminescence emission spectrum indicates the energy gap of 36.8 cm^(−1)between the ground state and the first excited state,consistent with the magnetic measurement results.1-Tb exhibits brilliant characteristic green light emission under UV light excitation.The absolute quantum yield of 1-Tb is 44.8%,and its first-order fitted decay lifetime is 779.21μs at room temperature.This study provides the way for directional construction of high-performance molecular materials with magnetic and optical dual-function.

Slow magnetic relaxation behaviors and diamagnetic dilution studies of a carboxyl bridged dinuclear dysprosium(Ⅲ) complex

By using a rigid bulky carboxylic ligand a-cyanocinnamic acid(CCA),a dinuclear dysprosium(Ⅲ) complex [Dy_(2)(CCA)_(6)(MeOH)_(4)](1) was synthesized.Single crystal X-ray crystallography reveals that the two eight-coordinate dysprosium ions are bridged by four deprotonated carboxyl groups,forming a centrosymmetric paddle-wheel-1ike structure.Dynamic magnetic property measurements indicate that complex 1 displays field-induced slow magnetic relaxation.The temperature-dependent relaxation times can be fitted using Orbach and Raman processes with parameters of n=2.8(2),C=27(8) s^(-1)/K^(n),τ_(0)=5(2) × 10^(-10) s and U_(eff)=40(3) cm^(-1).Magnetic studies on the diamagnetic Y~Ⅲ-diluted analogue[Dy_(0.206)Y_(1.794)(CCA)_(6)(MeOH)_(4)](2) reveal its slow magnetic relaxation behavior without external dc field and the antiferromagnetic coupling between the Dy^(Ⅲ) ions in 1.Fits on the obtained relaxation times of 2lead to the parameters of n=4.5(3),C=0.7(2) s^(-1)/K^(n),τ_0=2.8(2) × 10^(-9) s and U_(eff)=38(2) cm^(-1).The results suggest that slow magnetic relaxation originates from the single-ion relaxation of Dy^(Ⅲ) ions.Moreover,the diamagnetic dilution can suppress other fast relaxation pathways at low temperature,on account of the elimination of magnetic coupling and dipolar interaction.Ab initio calculations were then performed on the single Dy^(Ⅲ) ion species {YDy} and indicate that the first excited Kramers doublets(KDs)lie at ca.76 cm^(-1),which is slightly higher than the experimental U_(eff) value.The intramolecular magnetic interactions were also calculated and indicate a weak ferromagnetic dipole-diploe magnetic interaction and an antiferromagnetic exchange coupling.