Aggregation of [Ln III12] clusters by the dianion of 3-formylsalicylic acid. Synthesis, crystal structures, magnetic and luminescence properties†
Three isostrucutral dodecanuclear clusters with the general formula [Ln12(fsa)12(μf3-OH)12(DMF)12]·nDMF (fsa2− is the dianion of 3-formylsalicylic acid; Ln = Eu 1, Gd 2, Dy 3) have been obtained from the reaction of fromylsalicyclic acid (H2fsa), tetrabutylammonium hydroxide and Ln(NO3)3·6H2O in methanol/DMF. Their structure consists of four vertex-sharing heterocubanes. Each heterocubane unit is assembled from four LnIII ions, three μ3-OH groups and one μ3-oxygen atom arising from the fsa2− carboxylato group. The photophysical properties of the europium derivative investigated at both 300 and 80 K sustain a relative intense emission obtained under low power LED excitation at 420 nm. The dysprosium derivative shows a SMM behavior with an effective energy barrier Ueff of 22.9 cm−1, while the thermodynamical properties of Gd12 confirm a large magnetocaloric effect: S(7 T) − S(0 T) = 20R = 166 J mol−1 K), typical for isotropic GdIII derivatives, with ΔS = S(7 T) − S(0 T) = 1.7R for each GdIII ion.