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

Abstract

The reactions of the ditopic ligand 1,4-bis(2,2':6',2″-terpyridin-4'-yl)benzene (1) as well as the monotopic ligands 4'-phenyl-2,2':6',2″-terpyridine (2) and 2,2':6',2″-terpyridine (3) with Fe(2+), Co(2+), and Ni(2+) in solution are studied. While the reaction of 1 with Fe(2+), Co(2+), and Ni(2+) 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 Zn(2+) leads to an enhanced fluorescence of the terpyridine ligands. In contrast, Fe(2+), Co(2+), or Ni(2+) 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 and the full kinetic rate laws for the coordination of the terpyridine ligands 1, 2, and 3 to Fe(2+), Co(2+), and Ni(2+) are presented. The coordination occurs within a few seconds, and the rate constant increases in the order Ni(2+) < Co(2+) < Fe(2+). With the rate constants at hand, the polymer growth of Ni-MEPE is computed.

Two Series of Lanthanide Coordination Polymers and Complexes with 4′‐Phenylterpyridine and their Luminescence Properties

“…For the ligand 4′-phenyl-2,2′:6′,2′′terpyridine (ptpy), complexes especially with transition metals were studied. [18][19][20][21][22][23][24] Several examples of ptpy coordination compounds with rare earth metal ions are known, typically for 77 K. Alongside with standard ion-specific 4f-4f trivalent lanthanide luminescence in the visible and NIR (of emitters such as europium, terbium, dysprosium, neodymium, etc. ), visible range emission of praseodymium, holmium, erbium, and thulium was observed, which is rarely reported for coordination compounds.…”

TpyCo2+‐Based Coordination Polymers by Water‐Induced Gelling Trigged Efficient Oxygen Evolution Reaction

“…This phenomenon is strongly correlated to a series of metal‐to‐ligand charge transfer transitions. [ 20 ] By contrast, Co‐Mac‐3 and Co‐Mac‐4 shows higher‐intensity absorption bands centered at 320 nm, indicating that they are hexafunctional tpy‐based D 6h ‐symmetric self‐assembled polymers. [ 2c ]…”

The Kinetics of Growth of Metallo‐supramolecular Polyelectrolytes in Solution

“…A volume ratio of =0.913 is used, as discussed above, at a Co‐MEPE concentration of 4.8 g L −1 (=6.7 m m ). Since self‐assembly of ligand, L, and Co 2+ proceeds within seconds, it is not possible to obtain data within the first seconds of the reaction. For clarity, a data point at =0 is added corresponding to the molar mass of the monomer, that is [Co(L)] 2+ ⋅…”

“…Therefore, coordination of L with an excess of Zn 2+ leads to [Zn 2 (L)] 4+ complexes (see literature values of Ziessel et al . shown in Table ) since in this case K 1 >K 2 …”