Fine-Tuning of Magnetic Anisotropy in Tetranuclear M2Dy2 Complexes with Zig-Zag Topology: The Impact of 3d Metal Selection

This study presents the design, synthesis, and magnetic characterization of two novel heterometallic tetranuclear complexes, [M2Dy2(Hheb)2(heb)4]·4MeOH (H2heb = (E)-N′-(1-(2-hydroxyphenyl)­ethylidene)­benzohydrazide; M = Ni (1), Cu­(2)). These complexes exhibit a rare zig-zag core topology induced by the rigid Hheb/heb2– ligands. A subtle interplay between the incorporated 3d metal ions (Ni2+ and Cu2+) and the magnetic properties is evidenced. Notably, the choice of the 3d metal plays a crucial role in modulating the Dy3+ ion’s coordination environment and axiality, as supported by theoretical calculations. While both complexes exhibit rapid Quantum Tunneling of Magnetization (QTM), complex 1 (Ni2+) demonstrates markedly enhanced slow relaxation dynamics compared to complex 2. This difference is attributed to the stronger axiality indirectly induced by Ni2+ in complex 1, whereas the Cu2+-induced distortions and ferromagnetic interactions in complex 2 negatively affect the slow relaxation behavior.