CO-templated [LnNi] heterometallic compounds for enhanced magnetocaloric effects at low fields.

In the history of magnetochemistry development, lanthanide-transition (3d-4f) heterometallic compounds have been considered an attractive candidate for magnetic refrigerants. Herein, a series of heterometallic compounds have been designed and templated by CO anions, that is, {[LnNi(L)(CO)(HO)]·HO} [Ln = Gd (. Gd2Ni) = Sm (. Sm2Ni) = Tb (. Tb2Ni), HCO = oxalic acid; HL = ethylene diamine tetraacetic acid]. The structural analysis reveals that Ln2Ni compounds feature a CO-templated wavy-shaped two-dimensional layer. Then, adjacent wavy-shaped layers are further aggregated by CO anions, resulting in an innovative three-dimensional metal-organic framework. Magnetization analysis revealed that Gd2Ni exhibits a favorable -Δmaxm of 38.0 J kg K at 2.0 K for 7.0 T. In addition, the effect of weak ferromagnetic exchange interactions in Gd2Ni contributes to a decent magnetocaloric effect at low fields (-Δ = 25.1 J kg K at 2.0 T for 2.0 K and -Δ = 14.5 J kg K at 1.0 T for 2.0 K), outperforming most 3d-4f heterometallic compounds reported previously.