Side-Group Effect on the Slow Relaxations of {Dy} Single-Molecule Magnets with Confined NO Donors.

Deep insights into and substantial enhancement of the effective anisotropy energy barrier for magnetization reversal () are vitally important for the technological applications of dysprosium(III)-based single-molecule magnets (Dy-SMMs). To fully refine the ligand-field effect on spin relaxation, four centrosymmetric {Dy} entities with formula [Dy(CHOH)L(COO)] (HL 2-hydroxy-'-((pyridin-2-yl)methylene)benzohydrazide) have been solvothermally prepared by varying the side groups of carboxylate coligands (COO, = CF for , H for , CH for , and CpFe for ). Structural analyses reveal that all of the Dy carriers in have the same NO donor environments, and the non-coordinative groups attached to the equatorial carboxylate bridges have not substantially changed the binding ability of the shortest Dy-O bonds located at the axial position of the ligand field. Interestingly, the side groups have monotonically decreased the zero-field barriers of these weak antiferromagnetically coupled {Dy} analogues from 721 K down to 379 K. Further electronic structure calculations demonstrate that the main magnetic axes of are highly dominated by these comparable Dy-O short bonds, and the tensors have produced gradually increased transverse components responsible significantly for the decreased barriers. Additionally, thermally assisted relaxations occur preferably through the second (for ) and the first (for ) Kramer doublets. These interesting findings afford a new side-group effect to comprehensively understand the magnetostructural relationships and advance the rational design of high-performance Dy-SMMs.