Adaptability to Crystal Fields in a Series of COT/Monodentate Ligand-Based Dy and Er Single Ion Magnets.

Herein, Dy and Er, the typical oblate and prolate Kramers Ln ions, were employed to synthesize a series of isostructural pairs: - (Ln = Dy and Er). In the [(COT)Ln(THF)] cationic fragments of , central ions were coordinated by the equatorial ligand cyclooctatetraenyl (COT) and THF solvents, while in the heteroleptic complexes ((COT)Ln(OAr')), ((COT)Ln(OAr″)), and ((COT)Ln(N)), the coordination geometries were formed by the cooperation of COT and bulky aryloxides OAr' (2,6-bis(diphenylmethyl)-4-methylphenyl), OAr″ (2,6-bis(1-adamantyl)-4-methylphenyl), and amide N (bis(triisopropylsilyl) amide) for , , and , respectively. Among these complexes, with the combinations of varying coordination geometries and different anisotropies of f orbitals, , , and were found to be zero-field SIMs with effective energy barriers of 181.9, 527.7, and 622.0 K, respectively, which are consistent with the structural analyses and ab initio calculations. The blocking temperatures () of and are 4 and 7 K, respectively, as confirmed by the hysteresis loops at varying temperatures. The structures of exhibit an almost perfect umbrella-shaped geometry, characterized by N-Ln-Centroid (COT) angles measuring 178.9 and 179.3° for and , respectively. Crystallographic data from these structures were utilized to investigate the impact of ligand alignment on the magnetic properties of the compounds.