Utilizing 3d–4f Magnetic Interaction to Slow the Magnetic Relaxation of Heterometallic Complexes

The
synthesis, structural characterization, and magnetic properties of
four related heterometallic complexes with formulas [DyIII2CoII­(C7H5O2)8]·6H2O (1), [DyIII2NiII­(C7H5O2)8]·(C7H6O2)2 (2), TbIII2CoII­(C7H5O2)8 (3), and DyIII2CdII­(C7H5O2)8 (4) were reported. Each of complexes has a perfectly
linear arrangement of the metal ions with two terminal LnIII (LnIII = DyIII, TbIII) ions and
one central MII (MII = CoII, NiII, CdII) ion. It was found that 1–3 displayed obvious magnetic interactions between the spin
carriers according to the direct current (dc) susceptibility measurements.
Alternating current (ac) magnetic susceptibility measurements indicate
that complexes 1–4 all exhibit single-molecule
magnet (SMM) behavior, while the replacement of the diamagnetic CdII by paramagnetic ions leads to a significant slowing of the
relaxation thanks to the magnetic interactions between 3d and 4f ions,
resulting in higher relaxation barrier for complexes 1 and 2. Moreover, both Dy2Co
and Dy2Ni compounds exhibit dual relaxation pathways that
may originate from the single ion behavior of individual DyIII ions and the coupling between DyIII and CoII/NiII ions, respectively, which can be taken as the feature
of 3d–4f SMMs. The Ueff for 1 of 127 K is a relatively high value among the reported 3d–4f
SMMs. The results demonstrate that the magnetic coupling between 3d
and 4f ions is crucial to optimize SMM parameters. The synthetic approach
illustrated in this work represents an efficient route to design nd–4f based SMMs via incorporating suitable paramagnetic
3d and even 4d and 5d ions into the d–f system.