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.