摘要
In a series of COT/monodentate magneticcomplexes, withincreasing sizes of monodentate ligands, the centroid (COT)-Ln-O/Nconnection becomes more linear. @@@ Herein,Dy-III and Er-III, the typical oblateand prolate Kramers Ln ions, were employed to synthesize a seriesof isostructural pairs: 2-5Ln (Ln= Dy and Er). In the [(COT)-Ln-(THF)(4)](+) cationicfragments of 2Ln, central ions were coordinated by theequatorial ligand cyclooctatetraenyl (COT) and THF solvents, whilein the heteroleptic complexes 3Ln ((COT)-Ln-(OAr ')), 4Ln ((COT)-Ln-(OAr '')), and 5Ln ((COT)-Ln-(N-dagger dagger)), the coordination geometries were formedby 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-dagger dagger (bis-(triisopropylsilyl) amide) for 3Ln, 4Ln, and 5Ln, respectively. Among thesecomplexes, with the combinations of varying coordination geometriesand different anisotropies of f orbitals, 2Er, 3Dy, and 4Dy were found to be zero-field SIMswith 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 (T (B)) of 3Dy and 4Dy are 4 and 7 K, respectively, as confirmedby the hysteresis loops at varying temperatures. The structures of 5Ln exhibit an almost perfect umbrella-shaped geometry, characterizedby N-Ln-Centroid (COT) angles measuring 178.9 and 179.3 degrees for 5Dy and 5Er, respectively. Crystallographicdata from these structures were utilized to investigate the impactof ligand alignment on the magnetic properties of the compounds.
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单位北京大学