AZIDE ION AS A REDUCTANT OF Eu 3+ TO Eu2+

Abstract

The behavior of the Eu3+ /N3- system in dimethyl sulfoxide was studied using the spectral methods. It was found that a redox interaction occurs between the components of the system, leading to the formation of divalent europium ion. The reaction proceeds spontaneously, quickly, almost during the time of mixing the solutions. A wide band in the region of 320–400 nm with a maximum at 350 nm was detected in the absorption spectrum of the reaction products; while a wide structureless 350–450 nm emission band with a maximum at 380 nm, characteristic of the Eu 2+ ion, was observed in the photoluminescence (PL) spectrum. An increase in the optical density and PL intensity in these regions is accompanied by a decrease in the absorption and PL intensity of Eu3+ ion in the longer wavelength region of the spectrum. A possible scheme of chemical processes in the Eu3+ /N3- – DMSO system has been proposed, including: 1) replacement of the Cl- ion by an azide ion in the Eu3+ coordination sphere; 2) electron transfer from N3- to Eu 3+, leading to the reduction of the latter to the divalent state. The prerequisite for the occurrence of this stage of the reaction is the low electron affinity (–2.68 eV) of the azide radical intermediate compared to the relatively high redox potential of the Eu3+ /Eu2+ pair (–0.36 eV); 3) complexation of the resulting Eu 2+ ion with N3- ligand, which is accompanied by an increase in the optical density of the solution at a maximum of 350 nm. The possibility of this stage of the reaction has been confirmed experimentally: an in crease in the concentration of the chloride ion in the reaction mixture, as a competing ligand with N3- , leads to a decrease in the optical density of the solution. It has been proposed to use the reduction reaction of Eu3+ with azide ion as a simple method for the preparation of divalent lanthanides, since salts of azide acid are readily available compounds.