RESUMO
A novel dodecanuclear complex, [{(HL)(L)(DMF)Cu(II)Gd(III)(DMF)(H(2)O)}(6)]·6DMF (1; DMF = N,N-dimethylformamide), has been obtained using the ligand resulting from the condensation of 3-formylsalicylic acid with hydroxylamine (H(3)L). The exchange interaction between the phenoxo-bridged Cu(II) and Gd(III) ions is weak ferromagnetic (J = +1.01 cm(-1)). The combination of a high-spin ground state with small anisotropy leads to a significant magnetocaloric effect [-ΔS(m)(0-7 T) = 23.5 J K g(-1) K(-1) at â¼2 K].
RESUMO
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.
RESUMO
Two types of oxalato-bridged heterometallic 3d-4f dodeca- and hexanuclear compounds have been obtained by connecting six bi- and, respectively, trinuclear moieties through oxalato bridges arising from the slow decomposition of the L-ascorbic acid.