The different magnetic relaxation behaviors in [Fe(CN)6]3− or [Co(CN)6]3− bridged 3d–4f heterometallic compounds

Abstract

For investigating how different 3d ions influence the magnetic relaxation behaviors of 3d–4f systems, six isomorphic tetranuclear 3d–4f compounds of [LnFe(CN)₆(H₂L)(H₂O)(DMF)]₂·5H₂O (Ln = Dy(1), Tb(2), Ho(3), (H₂L = 2,6-diylbis(ethan-1-yl-1-ylidene)-di(isonicotinohydrazide))) and [LnCo(CN)₆(H₂L)(H₂O)(DMF)]₂·5H₂O (Ln = Dy(4), Tb(5), Ho(6)) were obtained from [M(CN)₆]³⁻ bridging Ln^III-Schiff-base units. The six isostructural compounds are all centrosymmetric with two nine-coordinated Ln^III ions in a muffin configuration and Cs symmetry. Magnetic analyses revealed that complex 1_DyFe with a weak antiferromagnetic Dy–Fe interaction does not show a slow magnetic relaxation behavior above 2 K, while diamagnetic Co^III ions in complex 4_DyCo enlarge the intermolecular Dy⋯Dy distance and induce ferromagnetic Dy–Dy interactions to suppress the quantum tunneling of the magnetization (QTM) and lead to the single-molecule magnet (SMM) behavior with an energy barrier of U_eff = 11.17 K in 1 KOe dc field. This paper gives another example of inducing paramagnetic 3d ions with weak 3d–4f coupling could not quench QTM effectively, while diamagnetic 3d ions could perform better.