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

Five decanuclear lanthanide-iron clusters, formulated as [Ln(2)Fe(8)(hmp)(10)(mu(2)-OH)(4)(mu(3)-OH)(2)(mu(4)-O)(4)(H2O)(6)]6ClO(4)xH(2)O (x approximate to 8, Ln = Y for 1; x approximate to 6, Ln = Dy for 2; x approximate to 6, Ln = Ho for 3; x approximate to 7, Ln = Tb for 4; x approximate to 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 tau(0) = 7.93 x 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.