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

Based on isomeric ligands, (2,4'-Hpcad = N-3-(2-pyridoyl)-4-pyridinecarboxamidrazone and 2,3'-Hpcad = N-3-(2-pyridoyl)-3-pyridinecarboxamidrazone), two carboxylate-bridged centrosymmetric Dy-III dimers, [Dy-2(2,4'-pcad)(2)(C2H3O2)(4)(H2O)(2)].4H(2)O (1) and [Dy-2(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 Dy-2 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.