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 DyIII 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 DyIII 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 (Ueff) of 53.5 K and 132.6 K, respectively, wherein compound 2 possesses the highest Ueff in nine-coordinated Dy2 compounds. Ab initio calculations of compound 2 for magnetic interactions, magnetic axes inclination and charge distribution around DyIII ions revealed simultaneous optimization of f–f interactions between the DyIII ions and the stronger ligand field axis of individual DyIII ion, which realizes excellent performance of 2. These findings demonstrate an efficient approach to enhancing the magnetic anisotropy barrier on using isomeric ligands.