Gd-based ferrocene complex with a large magnetocaloric effect from rapid room temperature synthesis

We report the fabrication of a novel heterometallic Gd-based ferrocene complex (Gd-Fc MOF) using 1,1′-ferrocenedicarboxylic acid (FDCA) as an organic ligand and gadolinium (III) nitrate hydrate as a metal ion source. Comprehensive investigation of the crystal structure and magnetic properties revealed a remarkable cryogenic magnetocaloric effect (MCE) near the liquefaction temperature of helium T = 2.5 K. Under a magnetic field change of ΔH = 7 T, the maximum entropy change (−ΔS_M^max) reaches to 49.19 J kg⁻¹ K⁻¹. This outstanding MCE arises from the synergistic interplay of the specific assembly structure, properties inherent to the FDCA ligand, and the large spin ground state of Gd³⁺. The Gd-Fc MOF exhibits significant promise for efficient cryogenic magnetic refrigeration in molecular-based systems. This potential arises from its high metal proportion, elevated theoretical magnetic entropy, rapid room-temperature synthesis capability, good magnetocaloric effect (MCE) performance near liquid helium temperatures, and a large calculated relative cooling power (RCP) of 460.7 J kg⁻¹, which demonstrates practical cooling capacity.