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 Dy^III ancillary ligand (hfac^– in the previously reported <bold>DyPyNO</bold> and tta^– in <bold>Dy</bold>). A clear hysteresis opening is visible at 0.5 K for <bold>Dy</bold> that allows for the determination of an antiferromagnetic (AF) coupling of –2.92 cm^–1 (<italic>S</italic> = 1/2, <italic>g</italic>_z = 19.58) which was confirmed by ab initio calculations. Comparison with the results of <bold>DyPyNO</bold> shows that stronger AF coupling correlates with better SMM behavior. This is further demonstrated by diamagnetic substitution, and a Y–Dy species (<bold>YDy</bold>) highlights that the strong AF magnetic interaction in <bold>Dy</bold> 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 <bold>Dy</bold>, namely <bold>161Dy</bold> and <bold>164Dy</bold>. [ABSTRACT FROM AUTHOR]