Solvent-free mechanochemical synthesis and magnetic properties of rare-earth based metal-organic frameworks

Abstract Mechanical milling of benzene 1,3,5-tricarboxylic acid [C 6 H 3 (COOH) 3 ], both with the single and mixed rare earth carbonates [R 2 (CO 3 ) 3 ·xH 2 O; R = Gd, Tb and Dy], leads to the formation of metal-organic frameworks [R{C 6 H 3 (COO) 3 }] that adopt MIL-78 type structure. M ( T ) data of the investigated MOFs do not show any apparent onset of long range magnetic ordering down to 2 K. The M ( H ) data for Gd{C 6 H 3 (COO) 3 }collected at 2 K show deviations from the magnetization behavior expected for non-interacting Gd 3+ ions. For the Gd based MOF the temperature dependence of the isothermal magnetic entropy change (i.e. magnetocaloric effect, Δ S M ) exhibits a monotonous increase with decreasing temperature and at T  = 3.5 K it reaches 34.1 J kg −1 K −1 for a field change (Δ H ) of 50 kOe. For the same Δ H the maximum values of Δ S M for R = Tb and Dy are 5.5 J kg −1 K −1 and 8.5 J kg −1 K −1 at 9.5 K and 4.5 K, respectively.