Three dinuclear lanthanide(III) compounds of a polydentate Schiff base ligand: Slow magnetic relaxation behaviour of the DyIII derivative

The initial employment of N-1,N-2,N-3,N-4-tri(3-methoxysalicylidene) triethylenetetraamine ligand (H3L, Scheme 1) in lanthanide coordination chemistry for single molecule magnets has yielded a new family of dinuclear Ln(2)(III) compounds with the general formula of [Ln(2)(L)(2)]center dot nCH(3)CN (Ln = Gd (1), Tb (2) with n = 0, Ln = Dy (3) with n = 4). These three complexes have been structurally and magnetically characterized. The structural analyses reveal that they are isomorphous dinuclear complexes where the Ln(2) entities were encapsulated by two polydentate Schiff base ligands. Variable-temperature magnetic susceptibility studies indicate the presence of dominant antiferromagnetic interactions in complexes 2 and 3, whereas complex 1 containing isotropic Gd ions allows the quantification of the antiferromagnetic interaction with J(Gd-Gd) = -0.041 cm(-1). Dynamic measurements reveal that 3 displays single-molecule magnet behaviour with an activation energy barrier Delta = 18.9 K and pre-exponential factor tau(0) = 3.92 x 10(-6) s, while 1 and 2 do not show any out-of-phase ac susceptibility signals.