Stability constants and molar absorptivities of rare earth complexes with 4-(2-pyridylazo)resorcinol

Complex formation of rare earths with 4-(2-pyridylazo) resorcinol (PAR) has been studied. Stability constants, molar absorptivities and thermodynamic functions for the complexes of rare earths with PAR have been estimated. Enthropy and enthalpy contributions to the stability constants have been evaluated. Nonmonotonic changes of the thermodynamic characteristics show that it is necessary to take into account the ionic and covalent nature of chemical bonds in the complexes as well as probable changes in the complex composition