Single-Molecule Magnet Behavior for an Antiferromagnetically Superexchange-Coupled Dinuclear Dysprosium(III) Complex

Abstract

A family of five dinuclear lanthanide complexes has been synthesized with general formula [Ln(III)(2)(valdien)(2)(NO(3))(2)] where (H(2)valdien = N1,N3-bis(3-methoxysalicylidene)diethylenetriamine) and Ln(III) = Eu(III)1, Gd(III)2, Tb(III)3, Dy(III)4, and Ho(III)5. The magnetic investigations reveal that 4 exhibits single-molecule magnet (SMM) behavior with an anisotropic barrier U(eff) = 76 K. The step-like features in the hysteresis loops observed for 4 reveal an antiferromagnetic exchange coupling between the two dysprosium ions. Ab initio calculations confirm the weak antiferromagnetic interaction with an exchange constant J(Dy-Dy) = -0.21 cm(-1). The observed steps in the hysteresis loops correspond to a weakly coupled system similar to exchange-biased SMMs. The Dy(2) complex is an ideal candidate for the elucidation of slow relaxation of the magnetization mechanism seen in lanthanide systems.

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

“…In all the three cases, the χ M T product decreases slightly between 300 and~50 K, before a more rapid decrease below~30 K, to reach values of 4.24(3), 9.52(4) and 11.02(5) cm 3 ·K·mol −1 at 2.0 K. For such Ln III ions with an unquenched orbital moment associated with a ligand field, the decrease of the χ M T product as the temperature is lowered can originate from the following possible contributions [50]: (a) the thermal depopulation of the Stark sublevels; (b) the presence of magnetic anisotropy; and (c) antiferromagnetic interactions between the Ln III centers. The relatively low χ M T values at 2.0 K may suggest the contribution of a weak to moderate Ln III ···Ln III interaction (Ln = Tb, Dy, Ho), as confirmed for the Gd III 2 complex 2.…”

“…As expected for pure Ln III systems, the exchange interaction is rather weak as a consequence of the shielded 4f orbitals that have small overlap with bridging ligand orbitals. This J value is typical for dinuclear complexes containing the {Gd III 2(μ2-OR)2} 4+ core [17,18,20,25,50]. Rov and Hughbanks performed a spin density functional (SDFT) study of dinuclear Gd III complexes containing the {Gd2(μ2-OR)2} 4+ core [20].…”

Direct measurement of dysprosium(III)˙˙˙dysprosium(III) interactions in a single-molecule magnet

“…5), but to simulate the low temperature w M T(T) and M(H) data, we need to account for a weak exchange interaction. One way to simulate such thermodynamic data for orbitally degenerate ions is the Lines model 27 , which employs an isotropic exchange between the spin component of the angular momenta (S ¼ 5 / 2 for Dy(III); see Methods) and has been used previously to model interactions between lanthanides 15,28 . Employing this model with PHI 29 we find J Lines ¼ þ 0.047(1) cm À 1 , which gives excellent fits to both w M T(T) and M(H) (Fig.…”

“…Radical bridging ligands can provide a strong magnetic exchange pathway between two lanthanide ions, leading to magnetic hysteresis at 14 K 3,4 . In other compounds weak Ln Á Á Á Ln interactions can shift the zero-field quantum tunnelling step to a finite field, known as exchange biasing 15 , with different effects on cryogenic magnetization curves depending on the sign of the exchange 16,17 or even mask single-ion slow relaxation modes 18 . More frequently, however, Ln Á Á Á Ln interactions increase quantum tunnelling rates, leading to apparently lower U eff values when compared with paramagnetic Ln ions doped into a diamagnetic lattice 8,17,19 .…”

Application of the Hubbard Model to Cp*2Yb(bipy), a Model System for Strong Exchange Coupling in Lanthanide Systems

“…Previous investigations have observed that exchange coupling can enhance SMM behavior in Ln complexes. 12,[32][33][34][35][36] Exchange coupling in Cp* 2 Yb(bipy) (3)…”