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(L₁^2–)₂(CO₃^2–)(MeOH)₂] complex 1-Dy₂, [Y₂(L₁^2–)₂(CO₃^2–)(MeOH)₂] complex 1-Y₂, [Dy₂(L₁^2–)₂(CO₃^2-)(MeOH)(TPPO)] complex 2-Dy₂, [Y₂(L₁^2–)₂(CO₃^2–)(MeOH)(TPPO)] complex 2-Y₂, [Dy₂(L₁^2–)₂(CO₃^2–)(TPPO)₂] complex 3-Dy₂, and [Dy₂(H₂L₂^2–)₂(CO₃^2–)(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 CO₃^2– 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 H₂L₂^2– 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.

We have synthesized axial carbonate-bridged Dy₂ complexes with N₃O₂ rigid equatorial planes and demonstrated the stepwise boosting and diminishing of the zero-field SMM behavior by replacing axial ligands and altering the bridging angle.