Formation of doubly charged transition metal-polyether-pyridyl mixed-ligand complexes by electrospray ionization

The formation of a series of doubly charged pyridyl ligand–polyether–transition metal complexes was studied using electrospray ionization (ESI) methods. Both doubly charged mixed-ligand dimer and trimers were observed. Differences in the electronic structures of the metal ions and the nature of the polyether and pyridyl ligands influence the types of complexes formed. Despite the large differences in the solution binding constants of pyridyl and polyether ligands, mixed-ligand complexes were efficiently formed, suggesting that the ESI process itself may enhance the formation of certain types of complexes that might not be favored in solution. Charge reduction of the metal ion within the mixed-ligand complexes was not observed, although charge reduction of Cu2+ occurred for the single-ligand polyether and pyridyl complexes.