Stabilization of Eu(II) tolls by macrocyclic compounds in the oxidation reaction with hydrogen peroxide

The influence of coronands 15C5 and 18C6 and cryptands 2.2.1 and 2.2.2 on t he chemiluminescence (CL) of the system Eu(II)/(III)-H2O2 was studied. Anal ysis of the chemiluminescence spectra revealed that the excited Eu(III) ion s are the dominant emitter in all cases. The stabilizing effect of the macr ocyclic compounds was manifested in an extension of the CL duration and was particularly strong in the systems with cryptands. The protective activity of ligands is explained by the matching of the ligand's cavity with the si ze of Eu(II) ions. Measurement of the Eu(II) absorption band decay (gamma = 248 nm) upon oxidation by hydrogen peroxide confirmed the results of the C L studies according to which the stabilizing properties of the macrocyclic ligands towards Eu(II) ions increase in the order 15C5 < 18C6 < 2.2.1 < 2.2 .2 in aqueous solution.