Wheel-like Ln₁₈ Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO₂

Two isostructural 2D MOFs ([Ln₇(CDA)₆(HCOO)₃(μ₃-OH)₆(H₂O)₈]_<i>n</i>, abbreviated as <b>1-Gd</b> and <b>2-Dy</b>) were successfully synthesized under solvothermal conditions. The self-assembly of lanthanide­(III) nitrate and 1,1′-cyclopropane-dicarboxylic acid (H₂CDA) resulted in wheel-like Ln₁₈ cluster second building units (SBU), which are further linked to six neighboring wheels to generate a 2D ordered honeycomb array. Both <b>1-Gd</b> and <b>2-Dy</b> exhibit high thermal stability and decompose above 330 °C. Moreover, they have good solvent stability in ten common solvents and pH stability with pH values from 1 to 13. Magnetic studies reveal that <b>1-Gd</b> exhibits weak antiferromagnetic coupling between adjacent Gd³⁺ ions and has a large magnetocaloric effect of 47.30 J kg^–1 K^–1 (Δ<i>H</i> = 7.0 T at 2 K), while <b>2-Dy</b> shows ferromagnetic interaction between adjacent Dy³⁺ ions. Interestingly, <b>1-Gd</b> and <b>2-Dy</b> can catalyze the cycloaddition of CO₂ to epoxides under mild conditions and can be reused at least five rounds with negligible loss of catalytic performance