Isomeric ligands enhance the anisotropy barrier within nine-coordinated {Dy2} compounds

Abstract

Based on isomeric ligands, (2,4′-Hpcad = N³-(2-pyridoyl)-4-pyridinecarboxamidrazone and 2,3′-Hpcad = N³-(2-pyridoyl)-3-pyridinecarboxamidrazone), two carboxylate-bridged centrosymmetric Dy^III dimers, [Dy₂(2,4′-pcad)₂(C₂H₃O₂)₄(H₂O)₂]·4H₂O (1) and [Dy₂(2,3′-pcad)₂(C₂H₃O₂)₄(H₂O)₂] (2), were obtained, where Dy^III ions adopted a monocapped square antiprism coordination geometry, but exhibiting different distortions. Fine-tuning the structure on using isomeric ligands had a significant impact on the magnetic properties of compounds 1 and 2. Magnetic studies revealed that 1 and 2 exhibit slow magnetic relaxation behaviours under a zero direct-current field exhibiting effective energy barriers (U_eff) of 53.5 K and 132.6 K, respectively, wherein compound 2 possesses the highest U_eff in nine-coordinated Dy₂ compounds. Ab initio calculations of compound 2 for magnetic interactions, magnetic axes inclination and charge distribution around Dy^III ions revealed simultaneous optimization of f–f interactions between the Dy^III ions and the stronger ligand field axis of individual Dy^III ion, which realizes excellent performance of 2. These findings demonstrate an efficient approach to enhancing the magnetic anisotropy barrier on using isomeric ligands.