Complexing properties of phenolic diazacrown ethers with transition and heavy metal ions

Abstract

Stability constants of complexes between phenolic diazacrown ether derivatives (L1-L6) and transition and heavy metal ions, i.e. Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺, were determined by UV spectrophotometric titration. Most of the systems studied exhibited ML complex formation, where a stability of complex increases, once substituents (R) extend, except for complexes of Ni²⁺ and Hg²⁺. It has been additionally observed that Pb²⁺ forms very strong complexes with every ligand studied (log βML ≽ 7) and exact stability constants cannot be determined except that of L6 (log βML = 6.17). A stability order for first-row transition metal ions is: Zn²⁺ < Ni²⁺ < Co²⁺ and that for IIB metal ions is: Zn²⁺ < Hg²⁺ < Cd²⁺. The exception is found in the system of LI where Hg²⁺ forms the most stable complex. It has been compared and found that cation selectivity order shows the same trend as the stability orders.