Enhancing the Magnetic Anisotropy in Low-Symmetry Dy-Based Complexes by Tuning the Bond Length.

One mononuclear complex [Dy(Htpy)(NO)(acac)] () and a tpy-extended 1D chain {[Dy(CHOH)(NO)(tpy)]·CHOH} () (Htpy = 4'-(4-hydroxyphenyl)-2,2':6',2''-terpyridine, Hacac = acetylacetone) were successfully designed to investigate the effect of bond length tuning around the Dy cation on the magnetic dynamics of single-molecule magnets (SMMs). Interestingly, two magnetic entities possess the same local coordination sphere (NO-donor) as well as the configuration (Muffin, ) of dysprosium centers. Only a slight difference in structure results from purposefully substituting the acetylacetone ligand in with hydroxyl oxygen from tpy linkage and one methanol molecule in . However, the remarkable differences in dynamics behavior were clearly found between them. Compound possesses a thermal-activated effective energy barrier (/) of 22.7 K under a 0 kOe direct current (dc) field and negligible hysteresis loop at 2.0 K, while complex shows high-performance SMM behavior with the largest energy barrier of 354.36 K among the reported nine-coordinated Dy-based systems and the magnetic hysteresis up to 4.0 K at a sweep rate of 200 Oe s. These experimental results combined with the previous reported data reveal that the shortest bond and the bond length difference around the Dy center synergistically determine the dynamics of SMMs. The uniaxial anisotropy increases with the decrease of the shortest bond and the increase of the bond length difference, which is confirmed by the theoretical calculations.