Nature of the magnetic interaction in the (Cu2+, Ln3+) pairs:: An empirical approach based on the comparison between homologous (Cu2+, Ln3+) and (NiLS2+, Ln3+) complexes

The reaction of {2,2'-[1-methyl-1,2-propanediyl bis(nitrilomethylidyne]-di(6-methoxyphenolato)}copper-(II) (LCu) or nickel(II) (LNi) with Ln(NO3)(3) in acetone led to strictly heterodinuclear [LCu(Me2CO)Ln(NO3)(3)] and [LNi(Me2CO)Ln(NO3)(3)] complexes (with Ln = all the lanthanides except prometheum: Ni in the low-spin state). Three complexes [(Cu2+, Ce3+), (Cu2+, Yb3+) and (Ni2+, Dy3+)] have been structurally characterized. They crystallize in the same monoclinic space groups P2(1)/c (no. 14) and are isomorphous. This relationship in conjunction with the diamagnetism of the Ni2+ ion allow an empirical evaluation of the effect of the crystal field on the magnetic properties as well as an approach towards the nature of the coupling between the copper(II) and the lanthanide(III) ions in the [LCu(Me2CO)Ln(NO3)(3)] complexes. The Cu-Ln interaction is antiferromagnetic for Ln = Ce-x Nd, Sm, Tm, and Yb, and ferromagnetic for Ln = Gd, Tb, Dy, Ho, and Er; however, the Cu-Pr and the Ctl-Eu pairs are devoid of any significant interaction along with the Cu - La and Cu - Lu pairs, in accordance with the nonmagnetic nature of the ground state for these lanthanide ions.