Fine-Tuning the SMM Properties of a Bis(ZnDy)-Based Compound by Rationally Reducing/Increasing the Electron Density in the Equatorial Plane Perpendicular to the O phenoxido –Dy-O phenoxido-bridges Direction

Five new bis(ZnDy) complexes with the general formula [Zn₂(μ-H₂L)₂(μ-dicarb)Dy₂(L')₂(L'')₂]X₂·solv were synthesized using Mannich bis(compartmental) ligand H₄L (highly phenoxido-containing macrocycle). Tetrafluorosuccinate (1, 3) and succinate (2, 4, 5) were used as dicarboxylates; ancillary ligands L' = NO₃⁻ (1), hfac (2 and 3), CF₃CO₂⁻/tfac (4), dbm (5); L'' = MeOH (4); and counterions X = NO₃⁻ (1) or OTf⁻ (2-5). All complexes have a similar axial environment defined by three phenoxido donors, while the equatorial ligand set was systematically tuned to control the electron density around DyIII. Magnetic measurements and ab initio calculations reveal a clear structure-property correlation: ligands that reduce the equatorial electron density stabilize the ground doublet MJ = ± 15/2 and provide enhanced SMM behavior and wider hysteresis loops (tetrafluorosuccinate and nitrate in 1 with UOrbach = 370 ± 30 K). More electron-donating ligands compress the Dy-O distances and reduce magnetic anisotropy, leading to weaker or absent SMM behavior. DyIII-centered emission was detected in all compounds, and analysis of the 482 nm band enabled the estimation of the splitting of the ⁶H15/2 ground term, which matches ab initio results. This confirms the internal consistency between spectroscopic and theoretical descriptions and reinforces the structure-magnetism correlation for these compounds.