Optimization of Magnetic Relaxation and Isotopic Enrichment in Dimeric DyIII Single‐Molecule Magnets

Single‐molecule magnet (SMM) behavior of dysprosium‐based dimers was optimized by substitution of a DyIII ancillary ligand (hfac– in the previously reported DyPyNO and tta– in Dy). A clear hysteresis opening is visible at 0.5 K for Dy that allows for the determination of an antiferromagnetic (AF) coupling of –2.92 cm–1 (S = 1/2, gz = 19.58) which was confirmed by ab initio calculations. Comparison with the results of DyPyNO shows that stronger AF coupling correlates with better SMM behavior. This is further demonstrated by diamagnetic substitution, and a Y–Dy species (YDy) highlights that the strong AF magnetic interaction in Dy significantly enhances magnetic relaxation at low temperature. This coupling is also expected to be at the origin of the unexpectedly weak isotopic effect observed for the isotopically pure parents of Dy, namely 161Dy and 164Dy.