Aggregation of [Ln III12] clusters by the dianion of 3-formylsalicylic acid. Synthesis, crystal structures, magnetic and luminescence properties

Abstract

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 Ln^III 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 U_eff 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 Gd^III derivatives, with ΔS = S(7 T) − S(0 T) = 1.7R for each Gd^III ion.