Unequivocal synthetic pathway to heterodinuclear (4f,4f′) complexes:: Magnetic study of relevant (LnIII, GdIII) and (GdIII, LnIII) complexes

The tripodal ligand tris[4-(2hydroxy-3-methoxyphenyl)-3-aza-3-buten]amine (LH3) is capable of coordinating to two different lanthanide ions to give complexes formulated as [LLnLn'(NO3)(3)].xH(2)O. The stepwise synthetic procedure consists of introducing first a Ln(III) ion in the inner N4O3 coordination site. The isolated neutral complex LLn is then allowed to react with a second and different Ln' ion that occupies the outer O-6 site, thus yielding a [LLnLn'(NO3)(3)].xH(2)O complex. A FAB(+) study has confirmed the existence of (Ln, Lri) entities as genuine, when the Ln' ion in the outer site has a larger ionic radius than the Ln ion in the inner site. The qualitative magnetic study of the (Gd, Ln) and (Ln, Gd) complexes, based on the comparison of the magnetic properties of (Gd, Ln) (or (Ln, Gd)) pairs and (Y, Ln) (or (Ln, La)) pairs, is very informative. Indeed, these former complexes are governed by the thermal population of the Ln(III) Stark levels and the Ln-Gd interaction, while the latter are influenced by the thermal population of the Ln(III) Stark levels. We have been able to show that a ferromagnetic interaction exists at low temperature in the (Gd, Nd), (Gd, Ce), and (Yb, Gd) complexes. In contrast, an antiferromagnetic interaction occurs in the (Dy, Gd) and (Er, Gd) complexes. Although we cannot give a quantitative value to these interactions, we can affirm that their magnitudes are weak since they are only perceptible at very low temperature.