A spectroscopic investigation of temperature effects on solution complexation in the Eu3+-acetate system

Europium-acetate complexation was studied using luminescence spectroscopy a s a function of temperature between 8 and 59 degrees C. The D-5(0)-->F-7(0) luminescence transition of Eu3+ was used to identify the presence of 1:1, 1:2, and 1:3 complexes with acetate in NaClO4 media. The results indicate a n increase in complexation for all three species with increasing temperatur e. An estimate of the stability quotient beta(1) for Eu(Ac)(2+) at 25 degre es C was obtained by observing changes in the intensity of its D-5(0)-->F-7 (0) transition as the acetate concentration was varied. A value of log beta (1) = 1.94 +/- 0.13 was obtained, consistent with reported stability quotie nts measured by other techniques. Although overall complexation increases w ith temperature, little change was observed in the distributions of the 1:1 , 1:2, and 1:3 complexes at constant ligand-to-metal ratios. (C) 2000 Elsev ier Science S.A. All rights reserved.