Magnetic field and dilution effects on the slow relaxation of {Er3} triangle-based arsenotungstate single-molecule magnets

Abstract

A triangular {Er₃} cluster containing polyoxometalate (POM), [Er₃(μ₃-OH)(H₂O)₈(AsW₉O₃₃)(AsW₁₀O₃₅(DL-mal))]₂²²⁻ (1) (mal = malate), has been obtained via one-pot reactions. Structural analyses demonstrate that three Er³⁺ ions bridged one μ₃-OH to generate a rare μ₃-OH-capped triangular {Er₃} cluster, which connects two different vacant polyanions to form an unsymmetrical sandwich-type subunit, and adjacent sandwiched subunits are linked through mal ligands to give the targeted dimer. When the Er³⁺ ions are substituted in whole or in part with Y³⁺ ions, the diamagnetic yttrium analogue [Y₃(μ₃-OH)(H₂O)₈(AsW₉O₃₃)(AsW₁₀O₃₅(DL-mal))]₂²²⁻ (2) and diluted sample [Er_0.15Y_2.85(μ₃-OH)(H₂O)₈(AsW₉O₃₃)(AsW₁₀O₃₅(DL-mal))]₂²²⁻ (Er@2) have also been synthesized. Magnetic studies reveal that 1 exhibits field-induced two-step magnetic relaxation processes; the slow relaxation process may arise from intramolecular magnetic interactions, whereas the fast one is likely to originate from the intermolecular dipole–dipole interactions supported by the magnetic results of Er@2. From ab initio calculations, it is found that although the magnetic anisotropies of 1 mainly originate from individual Er³⁺ fragments, the Er³⁺–Er³⁺ interactions have a considerable influence on their slow magnetic relaxation processes.