| Abstract
| - A step-by-step synthesis using a tripodal ligand with two coordination sites can yield hetero-dinuclear Ln−Ln‘ complexes; the first introduced Ln ion induces a proton migration, which is followed by a deprotonation in the next step, while the last step corresponds to the complexation of the second Ln ion in the outer coordination site of the ligand.
- The stepwise course of the synthesis of homo- (4f, 4f) and heterodilanthanide (4f, 4f ‘) complexes has beeninvestigated through structural determination of the intermediate and final products occurring in the process. In thefirst step, the tripodal ligand H3L is reacted with Ln(NO3)3·5H2O to give a complex (H3L)Ln(NO3)3 in which theligand does exist in a zwitterionic form. This unexpected feature has been definitely supported by a structuraldetermination performed on a closely related complex (HL‘)3Ln(NO3)3 (1). These species are fairly stable and maybe 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 thetrigonal 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Å, c = 42.982(2) Å, V = 21168(4) Å3, Z = 18.Complex 3 possesses a Dy(Ophenoxo)3Dy core, and a nitrato anion has been replaced by a η2-chelated o-vanillinanion. We did not succeed in obtaining crystals of any of the heterodinuclear LLnLn‘(NO3)3 entities, but theirexistence was unambiguously confirmed by positive fast atom bombardment mass spectrometry experiments.
|
