Single-molecule magnet behavior in heterometallic decanuclear [Ln2Fe8] (Ln = Y, Dy, Ho, Tb, Gd) coordination clusters

Abstract

Five decanuclear lanthanide–iron clusters, formulated as [Ln₂Fe₈(hmp)₁₀(μ₂-OH)₄(μ₃-OH)₂(μ₄-O)₄(H₂O)₆]·6ClO₄·xH₂O (x ≈ 8, Ln = Y for 1; x ≈ 6, Ln = Dy for 2; x ≈ 6, Ln = Ho for 3; x ≈ 7, Ln = Tb for 4; x ≈ 7, Ln = Gd for 5, Hhmp = 2-(hydroxymethyl)pyridine), have been synthesized and structurally characterized. Single-crystal structural analysis reveals that the cluster consists of six face-sharing defective cubane units. Dynamic magnetic investigations indicated that cluster 2 exhibits single-molecule magnet behavior under a zero dc field eliciting an effective energy barrier of U_eff = 17.76 K and a pre-exponential factor of τ₀ = 7.93 × 10⁻⁸ s. Investigation of the performance of a series of Fe^III–Dy^III SMMs indicates that the relatively low energy barrier in 2 is associated with the weak ferromagnetic coupling between Fe^III and Dy^III ions, while the strength of ferromagnetic interaction in these clusters is mainly related to the bond distances between Dy^III and O atoms coordinated to Fe^III ions. Clusters 3 and 4 exhibit similar dual relaxation pathways under their respective optimal external applied dc field, where the direct relaxation process occurs in the low-frequency area, which impedes the extraction of the U_eff, while the secondary relaxation process appears at a higher frequency, which is probably a connection with intermolecularly driven relaxation. Our findings offer a magneto-structural correlation model for further investigating the single-molecule magnet behavior in lanthanide–iron systems.