Chemical equilibria of lanthanides(Ln(III)=Pr, Sm, Gd, Dy)-macro-cyclic complexes with monodentate ligands in CH3OH(Part I)

Ln-macrocyclic((20)DOTA) complexes, (Ln((20)DOTA)NO3)(H2O))(NO3)2·xH2O(Ln(III)=Pr, Sm, Gd, Dy), which had been synthesized from 2, 6-diformyl-p-cresol(DFPC), was placed in methanol for 2 days, and (Ln((20)DOTA)(NO3)(CH3OH))2+ was formed. The equilibrium constants(K) for the substitution of coordinated CH3OH in the Ln-(20)DOTA complexes by various auxiliary ligands, La(=monodentate ligands; pyridine, imidazole, triethylamine, diethylamine, piperidine) were determined spectroscopically at 25. deg. C and 0.1 M. The pKa of auxiliary ligand is in the order of pyridine <imidazole<triethylamine<diethylamine<piperidine, however the K has shown the trend of pyridine<imidazole<diethylamine<piperidine<triethylamine