Investigation of Gd(III) 2D Metal-Organic Frameworks for Magnetic Refrigeration

The reaction between isophthalic acid (H₂L₁) and Gd(NO₃)₃·6H₂O leads to the formation of a two-dimensional (2D) extended framework with the molecular formula [Gd₂(L₁)₃(H₂O)₂]_n (1). Complex 1 crystallizes in monoclinic space group P2₁/n. The compound undergoes a reversible crystalline-to-amorphous phase transition. Magnetic susceptibility measurements on a polycrystalline sample of 1 reveal a weak ferromagnetic interaction between the Gd(III) centers below 20 K. Analysis of the magnetic data using the Fisher chain model indicates an exchange interaction strength (J) of +0.06 cm^-1. A significant magnetic entropy change (-ΔS_m) of 39.4 J kg^-1 K^-1 at 2.0 K and 9 T was observed, derived from detailed magnetization and heat capacity measurements on 1. The rate of change in the adiabatic temperature (ΔT_ad) was observed to be 2-3 K T^-1. Further, to infer the porosity within 1, a N₂ adsorption isotherm was conducted at 77 K, which indicates that the 2D sheets were held together strongly.