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

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)center dot 5H(2)O (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)center dot 5H(2)O (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 DyDy 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.