A kinetic and thermodynamic study of some lanthanide (III) complex formation reactions



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The stability constants for the formation of several one-to-one lanthanide (III) tartrate complexes have been determined at different temperatures. The rate constants for the formation of lanthanide (III) tartrate and oxalate complexes have also been obtained at different temperatures. The variation of thermodynamic parameters as a function of atomic number obtained in this study for lanthanide (III) tartrate complexes are explained in terms of the difference in hydration numbers between the lighter and heavier lanthanide elements. The kinetic parameters for the lanthanide (III) tartrate and oxalate systems are compared to those of other lanthanide systems reported in the literature. It is found that the structure of the ligand is significant in lanthanide complex formation reactions. For the lanthanide monodentate complexes such as the nitrates, sulfates and acetates, the reaction rate is controlled by the rate of water exchange of the cation, whereas for the lanthanide complexes with polydentate ligand anions such as the oxalate, tartrate and CyDTA (cyclohexylenediaminetetraacetate), the reaction rate is primarily determined by the chelate formation step. The lanthanide murexides and anthranilates which are monobasic polydentate ligand complexes may be an intermediate case between the above two cases.