Structure-Based Description of a Step-by-Step Synthesis of Homo- and Heterodinuclear (4f, 4f ) Lanthanide Complexes

The stepwise course of the synthesis of homo- (4f, 4f) and heterodilanthanide (4f, 4f ʹ) complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, the tripodal ligand H3L is reacted with Ln(NO3)3·5H2O to give a complex (H3L)Ln(NO3)3 in which the ligand does exist in a zwitterionic form. This unexpected feature has been definitely supported by a structural determination performed on a closely related complex (HLʹ)3Ln(NO3)3 (1). These species are fairly stable and may be isolated. In basic medium, (H3L)Ln(NO3)3 is deprotonated to yield a neutral LLn complex crystallized as LLnNaClO4 (2), the lanthanide ion being linked to the inner N4O3 coordination site of the ligand. Finally, addition of Lnʹ(NO3)3·5H2O (Lnʹ being similar or different from Ln) to the LLn complex yields the desired homoor heterodinuclear LLnLnʹ(NO3)3 complex 3, where the Lnʹ ion is coordinated to the outer O3O3 coordination site of the tripodal ligand.