Short-circuiting the slow relaxation barrier: Impact of local site distortion on the relaxation dynamics of a μ4-oxo-centered Dy4 square

The control of magnetic anisotropy and its spatial arrangement is a central challenge in the design of high-performance lanthanide-based single-molecule magnets (SMMs). Here, we report a μ ₄-oxo-centered tetranuclear dysprosium complex, [Dy₄( μ ₄-O)(Hbhmi)₂(bhmi)₂(acac)₄]·EtOH·H₂O, featuring a nearly square metallic core supported by proton-responsive Schiff-base ligands. The coexistence of two ligand protonation states induces significant electronic asymmetry, leading to four crystallographically independent Dy 3+ centers within the polynuclear complex. Magnetic measurements reveal dominant ferromagnetic-like interactions but no slow relaxation of the magnetization, even under an applied field. Ab initio calculations show that three Dy 3+ ions retain strong axial anisotropy, whereas a single distorted site introduces enhanced transverse components. The anisotropy axes are arranged in a radial, non-collinear fashion within the {Dy 4 } plane, resulting in a complex low-energy manifold driven by competitive magnetic interactions arising from non-collinear anisotropic exchange. These results highlight that, in this system, the combined effect of magnetic interactions and anisotropy misalignment is detrimental, leading to efficient relaxation pathways that suppress SMM behavior despite favorable single-ion properties.