The discovery that some metal coordination clusters may behave as single-molecule magnets (SMMs) [1][2][3][4] is currently stimulating abundant research in relation to potential applications in information processing and storage.[5] Indeed, SMMs are molecules that can be magnetized in a magnetic field and retain the magnetization when it is switched off. As a consequence, they may show hysteresis loops reminiscent of magnets.[2] In metal clusters, such behavior results from a strong magnetic ground state with large negative axial anisotropy (D < 0) [6,7] and induces two possible orientations (up and down), between which the magnetization can fluctuate. The fluctuation rate, also named relaxation, depends on the energy barrier U that separates the orientations. In the case of an ideal ground spin state S well separated from the excited states, U is equal to ÀD S 2 for an integer spin and ÀD(S 2 À 1 = 4 ) for a half-integer spin (D < 0). Therefore, the larger the D and S values are, the higher the barrier is and the longer the magnetization is retained. This barrier can be thermally overcome or shortcut by quantum tunneling of magnetization (QTM). [8] This tunneling trough the barrier contributes to accelerating the overall relaxation process. In practice, coexistence of the two processes leads to an experimental effective barrier U eff defined by an Arrhenius law: t = t 0 exp(U eff /k T).[9] One of the main goals of current research is to achieve long relaxation times t, which are crucial for information storage applications. [10,11] In this context, the use of lanthanide ions, such as Dy III and Tb III , has many advantages. Indeed, their large spins and pronounced spin-orbit coupling result in strong Ising-type magnetic anisotropy.[12] Recent reports have shown that even some of their mononuclear complexes may behave as SMMs. [13,14] During this work, a Dy III 3 trinuclear cluster was also reported to exhibit slow relaxation despite its near diamagnetic ground state.[15] Moreover, the combination of 3d and 4f transition-metal ions may increase the ground spin state through d-f magnetic interactions. [16][17][18][19][20] Lanthanides have high coordination numbers and geometries, which may be useful for engineering large polynuclear clusters, and their potential optical properties are of interest to prospective multifunctional materials. [21,22] With this in mind, and as part of our work on polynuclear metal complexes, [23,24] we chose the Schiff base 1,1,1-trifluoro-7-hydroxy-4-methyl-5-azahept-3-en-2-one (LH 2 , Scheme 1 (Figure 1 c) (Figure 1 b). This behavior affords distorted {Cu 2 L 2 Dy 2 (OH) 2 } cubane-like moieties in a similar way to homometallic cubane-like compounds. [25,26] The cationic entity can also be described as resulting from condensation of three distorted {Dy 2 Cu 2 O 4 } cubane-like moieties that share the Dy III ions in a triangular fashion. The structural features of the {Cu 2 L 2 Dy 2 (OH) 2 } moieties (Figure 1 c)
