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

Mechanical milling of benzene 1,3,5-tricarboxylic acid [C6H3(COOH)3], both with the single and mixed rare earth carbonates [R2(CO3)3·xH2O; R = Gd, Tb and Dy], leads to the formation of metal-organic frameworks [R{C6H3(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{C6H3(COO)3}collected at 2 K show deviations from the magnetization behavior expected for non-interacting Gd3+ ions. For the Gd based MOF the temperature dependence of the isothermal magnetic entropy change (i.e. magnetocaloric effect, ΔSM) exhibits a monotonous increase with decreasing temperature and at T = 3.5 K it reaches 34.1 J kg−1K−1 for a field change (ΔH) of 50 kOe. For the same ΔH the maximum values of ΔSM for R = Tb and Dy are 5.5 J kg−1K−1 and 8.5 J kg−1K−1 at 9.5 K and 4.5 K, respectively. [Display omitted] •Rare earth based MIL-78 type MOFs were prepared using a mechanochemical method.•The method described does not require solvents and a further purification.•Gd-TMA MOF exhibits extraordinarily high magnetocaloric effect.•The obtained MOFs show short range magnetic ordering below 20 K.