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 ‘) 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 (HL‘)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 Ln‘(NO3)3·5H2O (Ln‘ being similar or different from Ln) to the LLn complex yields the desired homo- or heterodinuclear LLnLn‘(NO3)3 complex 3, where the Ln‘ ion is coordinated to the outer O3O3 coordination site of the tripodal ligand. Complex 1 (Ln = La) crystallizes in the triclinic space group P1̄ (No. 2): a = 11.1883(7) Å, b = 11.8993(9) Å, c = 16.4197(10) Å, α = 81.900 (6)°, β = 79.406(5)°, γ = 79.470(6)°, V = 2099.5(2) Å3, Z = 2. Complex 2 (Ln = Eu) crystallizes in the monoclinic space group P21/n (No. 14): a = 13.6333(13) Å, b = 15.3799(12) Å, c = 17.1473(13) Å, β = 111.283(10)°, V = 3350.2(5) Å3, Z = 4. Complex 3 (Ln = Ln‘ = Dy) crystallizes in the trigonal space group R3̄ (No. 148) with a = b = 23.847(3) Å, c = 42.982(2) Å, V = 21168(4) Å3, Z = 18. Complex 3 possesses a Dy(Ophenoxo)3Dy core, and a nitrato anion has been replaced by a η2-chelated o-vanillin anion. We did not succeed in obtaining crystals of any of the heterodinuclear LLnLn‘(NO3)3 entities, but their existence was unambiguously confirmed by positive fast atom bombardment mass spectrometry experiments.