Kinetic Studies of the Coordination of Mono- and Ditopic Ligands with First Row Transition Metal Ions

The reactions of the ditopic ligand 1,4-bis(2,2':6',2 ''-terpyridin-4'-yl)benzene (1) as well as the mono topic ligands 4'-phenyl-2,2':6',2 ''-terpyridine (2) and 2,2':6',2 ''-terpyridine (3) with Fe2+, Co2+, and Ni2+ in solution are studied. While the reaction of 1 with Fe2+, Co2+, and results in metallo-supramolecular coordination polyelectrolytes (MEPEs), ligands 2 and 3 give mononuclear complexes. All compounds are analyzed by UV/vis and fluorescence spectroscopy. Fluorescence spectroscopy indicates that protonation as well as coordination to Zn2+ leads to an enhanced fluorescence of the terpyridine ligands. In contrast, Fe2+, Co2+, or Ni2+ quench the fluorescence of the ligands. The kinetics of the reactions are studied by stopped-flow fluorescence spectroscopy. Analysis of the measured data is presented the terpyridine ligands 1, 2, and 3 to Fe2+, Co2+, and Ni2+ are presented. The coordination occurs within a few seconds, and the rate constant increases in the order Ni2+ < Co2+ < Fe2+. With the rate constants at hand, the polymer growth of Ni-MEPE is computed.