Butterfly-shaped pentanuclear dysprosium single-molecule magnets.

Two new "butterfly-shaped" pentanuclear dysprosium(III) clusters, [Dy5(μ3-OH)3(opch)6(H2O)3]⋅3 MeOH⋅9 H2O (1) and [Dy5(μ3-OH)3(Hopch)2(opch)4(MeOH)(H2O)2]⋅(ClO4)2⋅6 MeOH⋅4 H2O (2), which were based on the heterodonor-chelating ligand o-vanillin pyrazine acylhydrazone (H2opch), have been successfully synthesized by applying different reaction conditions. Single-crystal X-ray diffraction analysis revealed that the butterfly-shaped cores in both compounds were comparable. However, their magnetic properties were drastically different. Indeed, compound 1 showed dual slow-relaxation processes with a transition between them that corresponded to energy gaps (Δ) of 8.1 and 37.9 K and pre-exponential factors (τ0) of 1.7×10(-5) and 9.7×10(-8)  s for the low- and high-temperature domains, respectively, whilst only a single relaxation process was noted for compound 2 (Δ = 197 K, τ0 = 3.2×10(-9)  s). These significant disparities are most likely due to the versatile coordination of the H2opch ligands with particular keto-enol tautomerism, which alters the strength of the local crystal field and, hence, the nature or direction of the easy axes of anisotropic dysprosium ions.