Boosting the mono-axial crystal field in stable high-coordinate Dy(iii) single-ion magnets by substitution of the phenoxy axial ligand

Abstract

Synthesis of air-stable and high-performance single-molecule magnets (SMMs) is challenging. Here, a heptadentate pentapyridyldiamine (BPA-TPA) ligand and fine-tuned axial phenoxy ligands are used to synthesize two triangular dodecahedral Dy(III) complexes [Dy(BPA-TPA)(4-methoxy-PhO)](BPh₄)₂·3CH₂Cl₂ (4) and [Dy(BPA-TPA)(2,4-dimethyl-PhO)](BPh₄)₂·0.85CH₂Cl₂ (5). Both complexes have high effective barriers exceeding 400 K and magnetic hysteresis up to 8 K, which is ascribed to one strong and short Dy–O bond combined with seven weak Dy–N bonds. Ab initio calculations reveal the thermally activated quantum tunneling of magnetization through the first excited Kramers doublet, due to the presence of a strong axial Dy–O crystal ligand. Substitution of the phenoxy ligand leads to more constrained vibrations, improving the magnetic hysteresis behavior for 5.