Potentiometric and spectrophotometric studies of the equilibria between silver(I) ion and crown ethers containing chromophore substituents in propylene carbonate

Abstract

Potentiometric and UV-spectrophotometric methods have been used to study the coordination properties of crown ethers and their derivatives containing 9,10-dioxo-1-anthryl, 8-hydroxy-9,10-dioxo-1-anthryl and 8-tosyloxy-9,10-dioxo-1-anthryl substituents with respect to the silver(I) ion in propylene carbonate. It was found that unsubstituted crown ligands were capable of forming two types of complex ion. The silver(I) ion can enter the macrocycle cavity forming 1∶1 complexes or can coordinate externally to the nitrogen atom of a ligand as occurs for typical complexes of silver(I) with nitrogen ligands. This results in Ag(crown)₂⁺ complexes. Introduction of chromophore groups allows investigation of the mechanism of AgL⁺ and AgL₂⁺ complex formation by spectrophotometric methods. Attaching a bulky chromophore to the nitrogen atom of the aza-crown makes the formation of the AgL₂⁺ complexes for monoaza-crown-15 strongly restricted or impossible. For 13-(9,10-dioxo-1-anthryl)-1,4,7,10-tetraoxa-13-azacyclopentadecane (A₂15C5AQN) the presence of only one substituent leads to an increase in the stability of the external complex (AgL₂) and the formation of other complex structures Ag₂L₃²⁺ and Ag₃L₂³⁺.