Magnetocaloric effect and slow magnetic relaxation behavior in binuclear rare earth based RE2(L)2(DMF)4 (RE = Gd, Tb, and Dy) complexes

Three binuclear rare earth based complexes combining RE ions with semirigid tricarboxylic ligand (H3L), namely, [RE2(L)2(DMF)4] [RE = Gd, Tb, and Dy; H3L = 5-((4-Carboxybenzyl)oxy)isophthalic acid; DMF = N,N-dimethylformamide] complexes, were fabricated successfully. The RE2(L)2(DMF)4 complexes consist of two central RE ions with the same coordination environment which were connected by two tridentate bridging carboxylic groups and two syn-syn bidentate bridging carboxylic groups originating from the L3– ligands to form the {RE2} dimeric unit. And thus provides the basis for further constructing a dense three-dimensional (3D) network structure. Moreover, the present RE2(L)2(DMF)4 complexes can be described by a topology diagram with the topology point symbol of {42·6}2{44·62·87·102}. Weak anti-ferromagnetic (AFM) coupling between the adjacent RE ions for all the present complexes is found according to the magnetic calculations. The observed significant cryogenic magnetocaloric effect (MCE) with the maximum magnetic entropy change − Δ S M m a x to be 26.3 J/(kg·K) with Δ H = 7 T in Gd2(L)2(DMF)4 complex makes it competitive for the cryogenic magnetic refrigerant. Moreover, the slow magnetic relaxation behavior at 0.2 T dc field with an obvious large U e f f / k = 45(4) K and τ 0 = 6.5(2)×10−10 s is confirmed in Dy2(L)2(DMF)4 complex. This work not only provides an effective strategy for obtaining molecular materials with high MCE, but also confirms that tricarboxylate ligands are the ideal choice for constructing stable high dimensional geometric structures.