3.2. Complexation studies of Eu3þ–BA in MeCN
To understand the geometry of Eu3þ–BA in MeCN, a detailed
study on the complexation has been performed and the result is
summarized below.
3.2.1. UV–vis spectroscopy
For complexation studies of Eu3þ with benzoate, absorption
spectra were recorded by titration of benzoate with Eu3þ ion in
MeCN. Fig. 3 shows the absorption spectra of 1 104 M BA with
different concentrations of Eu3þ ion (0.0–4.66 105 M) in MeCN
medium at pH 4.5. The absorption spectrum of BA without Eu3þ
shows maximum at 226 nm in MeCN. Complexation of benzoate
ion with Eu3þ results an increase in absorbance along with a
gradual red-shift in the absorption maximum. It appears that
complex stabilizes the electronic excited state of europium benzoate
more compared to ground state causing red-shift in absorption
maximum.
The stoichiometry of the Eu3þ–BA complex was determined
from the absorption spectra (Fig. 3) by applying the mole ratio
method [32–34]. The absorbance of Eu3þ–BA measured at 231 nm
is plotted in Fig. 4 as a function of mole ratio (Eu3þ to benzoate).
The intersection of two tangents of the absorbance data occurs at a
molar ratio of 0.33, which indicates the formation of ML3 type
complex by Eu3þ–BA in MeCN. The stability constant of the above
complex was calculated from these absorption spectra using the
program HypSpec 2009 [35]. The log β of the ML3 complex was
computed to be 12.5570.25 (Table 2).