MIIIDyIII3 (M = FeIII, CoIII) Complexes: Three-Blade Propellers Exhibiting Slow Relaxation of Magnetization

[DyIII(HBpz3)2]2+ moieties (HBpz3– = hydrotris(pyrazolyl)borate) and a 3d transition-metal ion (FeIII or CoIII) have been rationally assembled using an dithiooxalato dianion ligand into 3d-4f [MDy3(HBpz3)6(dto)3]·4CH3CN·2CH2Cl2 (M = Fe (1), Co (2) complexes. Single-crystal X-ray studies reveal that three eight-coordinated DyIII centers in a square antiprismatic coordination environment are connecting to a central octahedral trivalent Fe or Co ion forming a propeller-type complex. The dynamics of the magnetization in the two isostructural compounds, modulated by the nature of the central MIII metal ion, are remarkably different despite their analogous direct current (dc) magnetic properties. The slow relaxation of the magnetization observed for 2 mainly originates from isolated Dy ions, since a diamagnetic CoIII metal ion links the magnetic DyIII ions. In the case of 1, the magnetic interaction between S = 1/2 FeIII ion and the three DyIII magnetic centers, although weak, generates a complex energy spectru...