A series of dinuclear Dy(III) complexes bridged by 2-methyl-8-hydroxylquinoline: replacement on the periphery coordinated beta-diketonate terminal leads to different single-molecule magnetic properties

摘要

A series of HMq-bridged dinuclear dysprosium complexes, namely, (Dy(acac)(2)(CH3OH)](2)(11-HMq)(2) (1), [Dy(DBM)(2)](2)(mu-HMc1)(2)(n-CEHIA) (2), [Dy(hmac)(2)(2)(mu-HMq)(2) (3) and [Dy(hfac)(3)](2)(mu-HMq)(2) (4) (HMq = 2-methyl-8-hydroxyquinoline, acac = acetylacetone, DBM = dibenzoylmethane, hmac = hexamethylacetylacetonate and hfac = hexafluoroacetylacetonate), were structurally and magnetically characterized. X-ray crystallographic analyses of the structures reveal that HMq serves as the effective bridge to link two Dy(iii) centers by means of the phenoxyl oxygen and nitrogen atoms and the periphery p-diketonate ligands complete the coordination sphere by bidentate oxygen atoms. The different substituents on the li-diketonate terminal lead to different coordination models mostly due to the steric hindrance of these substituents, and the electron -withdrawing or donating effects likely influence the strength of the ligand fields and the Dy(iii) ion anisotropy. Measurements of alternating-current (ac) susceptibility on complexes 1-4 reveal that complexes 3 and 4 display significant zero-field single-molecule magnetic (SMM) behavior with barrier energy U-eff/kB = 14.8 K, To = 1.8 x 10(-5) s and U-eff/k5 = 9.2 K, To = 1.7 x 10(-5) s, respectively, whereas 1 and 2 exhibit field-induced SMM behavior, and these differences are attributed to the alteration on the periphery li-diketonate ligands. Their distinct slow magnetic relaxation behaviors were related to their different individual Dy(iii) ion magnetic anisotropy and intramolecular coupling, which were confirmed by ab initio calculations.