LUMINESCENCE OF DIVALENT EUROPIUM COMPLEXES WITH N-PIVOT LARIAT AZACROWN ETHERS

The luminescence and absorption spectra and emission lifetimes of divalent europium complexes with 10-(2-methoxyethyl)-1,4,7-trioxa-10-azacyclododecane (MEN12C4) and 13-(2-methoxyethyl)-1,4,7,10-tetraoxa-13-aza-cyclopentadecane (MEN15C5) have been investigated. The stoichiometry of the Eu2+ N-pivot lariat monoaza-crown ether complexes in methanol was determined by the use of the emission intensity molar ratio method and by monitoring the shift and splitting of the proton magnetic resonances for the Sr2+ analogs. These results indicated the formation of the strongly bound 1:1 Eu2+ complex with MEN15C5. It was also found that the 1:2 Eu2+-MEN12C4 complex was formed in the presence of excess ligand and that the 1:1 complex was predominantly formed for the ratio of MEN12C4:Eu2+ less-than-or-equal-to 1. Furthermore it was revealed that the oxygen atom in the 2-methoxyethyl group also coordinated to the Eu2+ ion. Luminescence intensity was enhanced by the complexation, compared with that for the Eu2+ ion solvated by methanol. The luminescence intensities for both the 1:2 Eu2+-MEN12C4 and the 1:1 Eu2+-MEN15C5 complex were 410 and 13 times greater than that given by a methanolic EuCl2 solution of the same Eu2+ concentration (4 x 10(-3) M), respectively. The emission intensity for the Eu2+-MEN12C4 complex was larger than that obtained for any other Eu2+ macrocyclic ligand complex having nitrogen as coordinating atoms.