Structures and Single-Molecule Magnet Behavior of Dy₃ and Dy₄ Clusters Constructed by Different Dysprosium(III) Salts

Using the Schiff base ligand H₂L-pyra (<i>N</i>'-(2-hydroxybenzoyl)pyrazine-2-carbohydrazonamide) with multiple dentate sites, the trinuclear Dy^III-based complex [Dy₃(HL-pyra)₂(L-pyra)₂(CH₃COO)₃]·2H₂O (<b>1</b>) was synthesized. By analyzing the fragmented assembly process and fine-tuning the bridging anions, complex [Dy₄(HL-pyra)₂(L-pyra)₄(NO₃)₂(H₂O)₂]·8H₂O (<b>2</b>) with different nuclear numbers was successfully synthesized. Magnetic studies demonstrated that <b>1</b> did not exhibit magnetic relaxation behavior under the external field; however, <b>2</b> exhibited zero-field single-molecule magnetic relaxation behavior with an effective energy barrier (<i>U</i>_eff) of 197.44 K. This is attributed to the improved anisotropy of the single ion after the normalization of the crystal structure, thus realizing the molecular magnetic switching. Moreover, magnetic dilution analysis of <b>2</b> demonstrated that the weak magnetic interaction between metal ions inhibited the occurrence of quantum tunneling of magnetization (QTM), resulting in high-performance single-molecule magnet (SMM) behavior. The reasons for the magnetic difference between these two complexes were analyzed using <i>ab initio</i> calculation and magneto-structural correlations. This study provides a reasonable prediction of the ideal configuration of the approximately parallelogram Dy^III-based SMMs, thus offering an effective approach for synthesizing Dy₄ complexes with excellent properties.