Rare earth metal complexes based on a tripodal ligand and their application as highly selective “turn-on” fluorescent probe for Fe3+ ion

A C3-symmetric tripodal ligand, 1,1′,1″-(nitrilotri-2,1-ethanediyl)tris-2(1H)-pyridinone (ntetp), has been designed and synthesized. Two families of isostructural rare earth coordination complexes have therefore been constructed based on this ligand, namely [M(ntetp)(NO3)3]n [M = Y(1), La(2), Ce(3), Pr(4), Sm(5), Gd(6), Dy(7), Ho(8)] and [M(ntetp)Cl3]n [M = Tb(9), Er(10), Yb(11), Lu(12)]. Single-crystal analyses reveal that both series of complexes bear one-dimensional chain structures, with the metal centers taking nine-coordinate geometry in 1–8 and distorted octahedral geometry in 9–12. Solutions of the selected representative complexes 1 and 10 show highly selective fluorescent enhancement toward Fe3+ ion, comparing to non-significant response toward Ca2+, Co2+, Zn2+, Cr3+, Mn2+, Ni2+, Cu2+, Cd2+, Li+, Na+, Al3+, K+, Ba2+ and Mg2+ ions. Also, the fluorescent enhancement induced by Fe3+ ion is not affected by the above-mentioned ions, demonstrating promising capabilities of complexes 1 and 10 as “turn-on” fluorescent probe.