Sequential Synthesis of 3d–3d′–4f Heterometallic Heptanuclear Clusters in between Lacunary Polyoxometalates

In
this work, we have successfully created several unprecedented
discrete 3d–3d′–4f heterotrimetallic clusters
in between lacunary polyoxometalates (POMs). By the three-step sequential
introduction of metal cations into a trivacant lacunary POM TBA4H6[A-α-SiW9O34] (TBA
= tetra-n-butylammonium) in organic media, five kinds
of sandwich-type POMs with double-diamond-shaped 3d–3d′–4f
heptanuclear clusters (IIIFeM4Ln2, TBAnHm­[FeM4­{Ln­(L)2}2­O2­(A-α-SiW9O34)2], M = Mn3+, Cu2+; Ln = Gd3+, Dy3+, Lu3+;
L = acac (acetylacetonate), hfac (hexafluoroacetylacetonate)) were
successfully synthesized for the first time. By introduction of two
[Ln­(L)2]+ units on the ends of pentanuclear
clusters [FeMn4O18(OH)2]23– and [FeCu4O18(OH)2]27–, the magnetic interactions between Mn3+–Mn3+ and Cu2+–Cu2+ could be modulated.
Among a series of the heterometallic heptanuclear compounds, IIIFeMn4Lu2 exhibited the slow magnetic
relaxation characteristic for a single-molecule magnet under the zero
applied magnetic fields.