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 [R-2(CO3)(3)center dot xH(2)O; 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 noninteracting Gd3+ ions. For the Gd based MOF the temperature dependence of the isothermal magnetic entropy change (i.e. magnetocaloric effect, Delta 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 (Delta H) of 50 kOe. For the same Delta H the maximum values of Delta 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. (C) 2016 Elsevier B.V. All rights reserved.