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

A family of five dinuclear lanthanide complexes has been synthesized with general formula [Ln(2)(III)(valdien)(2)(NO3)(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.