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.本研究成功在缺位多金属氧酸盐（lacunary polyoxometalates, POMs）的空隙间构筑了多种前所未有的离散型3d–3d′–4f异三金属簇。通过在有机介质中向三缺位多金属氧酸盐TBA4H6[A-α-SiW9O34]（TBA=四正丁基铵，tetra-n-butylammonium）中依次三步引入金属阳离子，我们首次成功合成了五种带有双菱形结构3d–3d′–4f七核金属簇的夹心型多金属氧酸盐，其对应编号为IIIFeM4Ln2，通式为TBAnHm[FeM4{Ln(L)2}2O2(A-α-SiW9O34)2]，其中M=Mn³+、Cu²+；Ln=Gd³+、Dy³+、Lu³+；L=acac（乙酰丙酮根，acetylacetonate）、hfac（六氟乙酰丙酮根，hexafluoroacetylacetonate）。通过在五核金属簇[FeMn4O18(OH)2]²3–和[FeCu4O18(OH)2]²7–的两端引入两个[Ln(L)2]+单元，可对Mn³+与Mn³+、Cu²+与Cu²+之间的磁相互作用进行调控。在一系列异金属七核化合物中，IIIFeMn4Lu2在零外磁场条件下展现出单分子磁体（single-molecule magnet）特有的慢磁弛豫特性。