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]<i>_n</i> (<b>1</b>). Complex <b>1</b> crystallizes in monoclinic space group <i>P</i>2₁<i>/n</i>. The compound undergoes a reversible crystalline-to-amorphous phase transition. Magnetic susceptibility measurements on a polycrystalline sample of <b>1</b> 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 (<i>J</i>) of +0.06 cm^-1. A significant magnetic entropy change (-Δ<i>S</i>_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 <b>1</b>. The rate of change in the adiabatic temperature (Δ<i>T</i>_ad) was observed to be 2-3 K T^-1. Further, to infer the porosity within <b>1</b>, a N₂ adsorption isotherm was conducted at 77 K, which indicates that the 2D sheets were held together strongly.