Lanthanide complexes of polyacid ligands derived from 2,6-bis(pyrazol-1-yl)pyridine, pyrazine, and 6,6'-bis(pyrazol-1-yl)-2,2'-bipyridine: Synthesis and luminescence properties

The synthesis of three novel pyrazole-containing complexing acids, N,N,N',N'-{2,6-bis[3-(aminomethyl)pyrazol-1-yl]-4-methoxypyridine}tetrakis{acetic acid) (1), N,N,N',N'-{2,6-bis[3-(aminomethyl)pyrazo-1-yl]pyrazine}-tetrakis(acetic acid) (2), and N,N,N',N'-{6,6'-bis[3-(aminomethyl)pyrazol-1-yl]-2,2'-bipyridine}tetrakis(acetic acid) (3) is described. Ligands 1-3 formed stable complexes with Eu-III, Tb-III, Sm-III, and Dy-III in H2O whose relative luminescence yields, tripler-state energies, and emission decay lifetimes were measured. The number of H2O molecules in the first coordination sphere of the lanthanide ion were also determined. Comparison of data from the Eu-III and Tb-III complexes of 1-3 and those of the parent trisheterocycle N,N,N',N'-{2,6-bis[3-(aminomethyl)pyrazol-l-yl]pyridine}tetrakis(acetic acid) showed that the modification of the pyridine ring for pyrazine or 2,2'- bipyridine strongly modify the luminescence properties of the complexes. MeO Substitution at C(4) of 1 maintain the excellent properties described for the parent compound and give an additional functional group that will serve for attaching the label to biomolecules in bioaffinity applications.