Complexation Reactions between N,N '-Diethyl-N,N '-Difluorophenyl-2,2'-Bipyridyl-6,6-Dicarboxamides with Europium in Ethanol: Spectrophotometric and Isothermal Titration Calorimetry Studies

In this work, we studied the thermodynamic parameters of the complexation reaction between europium and N,N '-diethyl-N,N '-difluorophenyl-2,2'-bipyridyl-6,6'-dicarboxamides in ethanol. The complexation reaction lead to one complex particle with 1 : 1 metal : ligand composition. Spectrophotometric and calorimetric titration methods were used for determination of the stability of complexes. According to our data, the fluorine atom in the meta-position in the ligand (log K = 3.59) increases the stability of complexes, enthalpy and entropy compared with the para-position (log K = 3.26). Comparison of two parameters ΔrH and TΔrS for the 3-F ligand (–8.6 and 14.15 kJ/mol, respectively) shows that they are lower than that of for the 4-F ligand (–15.5 and 10.19 kJ/mol, respectively).