A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)(n)](-) complexes

作者：Janicki Rafal^*; Mondry Anna

来源：Physical Chemistry Chemical Physics, 2014, 16(48): 26823-26831.

DOI：10.1039/c4cp04093g

Two anionic complexes [Er(EDTA)(H2O)(2)](-) and [Er(EDTA)(H2O)(3)](-) were obtained in the form of the following compounds: [C(NH2)(3)](2)[Er(EDTA)(H2O)(2)]ClO4 center dot 6H(2)O (I) and Na[Er(EDTA)(H2O)(3)]center dot 5H(2)O (II), respectively. The UV-vis-NIR absorption spectra of both monocrystals were measured at room temperature and at 4.2 K. The influence of the coordination number changes on intensities of the f-f transitions and the crystal field splitting of L-2S+1(J) multiplets are discussed. The weighted sum of molar absorption coefficients of f- f transitions in the spectra of I and II was used to reproduce the absorption bands of the Er3+-EDTA complex in aqueous solution. This approach allowed us to estimate that the complex in solution exists in 95% as the 8-coordinate [Er(EDTA)(H2O)(2)](-) species and in 5% as the 9-coordinate [Er(EDTA)(H2O)(3)]-ones as well as to calculate the conditional hydration equilibrium constant (K-aqua) of the reaction: [Er(EDTA)(H2O)(3)](-) <-> [Er(EDTA)(H2O)(2)](-) + H2O which is rather difficult to determine by using other methods. The K-aqua value was found to be 19 +/- 1.

• 出版日期2014