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

Potentiometric and UV-spectrophotometric methods have been used to study th e 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-di oxo-1-anthryl substituents with respect to the silver(I) ion in propylene c arbonate. It was found that unsubstituted crown ligands were capable of for ming two types of complex ion. The silver(I) ion can enter the macrocycle c avity 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 chromo phore groups allows investigation of the mechanism of AgL+ and AgL2+ comple x formation by spectrophotometric methods. Attaching a bulky chromophore to the nitrogen atom of the aza-crown makes the formation of the AgL2+ comple xes for monoaza-crown-15 strongly restricted or impossible. For 13-(9,10-di oxo-1-anthryl)-1,4,7,10-tetraoxa-13-azacyclopentadecane (A(2)15C5AQN) the p resence of only one substituent leads to an increase in the stability of th e external complex (AgL2) and the formation of other complex structures Ag2 L32+ and Ag3L23+.