Complexing Properties of Phenolic Diazacrown Ethers with Transition and Heavy Metal Ions

The complexation equilibria of the phenolic diazacrown ether derivatives L1–L11 with transition and heavy metal ions (Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+) have been studied in methanol using UV absorption spectrophotometry. A majority of the systems studied formed only ML complexes. Using a ligand with a different position of the substituents on the phenolic side arms (denoted L7) leads to ML2 formation with most of the metal ions. Every ligand forms very strong ML and ML2 complexes with Pb2+, and, in nearly all cases, only a lower limit could be derived for the stability constant. The stability of the complexes generally increases as the length of the para-substituents on the phenol groups increases. Among the metal ions tested, Zn2+ and Hg2+ are the least preferred by alkyl and alkoxy derivatives, respectively.