Axial Carbonate-Bridged Dy₂ Complexes Having Rigid N₃O₂ Equatorial Planes: Stepwise Boosting and Tuning of the Zero-Field SMM Behavior

Herein, we report the synthesis of carbonate-bridged binuclear Ln(III) complexes [Dy2(L12–)2(CO32–)(MeOH)2] complex 1-Dy2, [Y2(L12–)2(CO32–)(MeOH)2] complex 1-Y2, [Dy2(L12–)2(CO32-)(MeOH)(TPPO)] complex 2-Dy2, [Y2(L12–)2(CO32–)(MeOH)(TPPO)] complex 2-Y2, [Dy2(L12–)2(CO32–)(TPPO)2] complex 3-Dy2, and [Dy2(H2L22–)2(CO32–)(TPPO)2] complex 4-Dy2, having a rigid equatorial pentagonal plane around each Ln(III) ion. The Schiff base H2L1 (2,6-diacetylpyridine bis-benzoyl hydrazone) and H4L2 (2,6-diacetylpyridine bis-salicyl hydrazone) ligands were used to provide a rigid equatorial pentagonal plane to the Ln(III) ions through their N3O2 donor atoms. One of the axial sites of each Ln(III) is occupied by triphenylphosphine oxide (TPPO) or methanol ligand, while CO32– occupies the other axial sites. The successful replacement of axially coordinated methanol by the TPPO ligand boosted the zero-field SMM property in 3-Dy2. We observed that phenolic −OH in H2L22– ligands imposes significant structure orientation in 4-Dy2 compared to 3-Dy2 and tunes the zero-field SMM properties by altering the Dy1-O-Dy2 bridging angle.