title: Copper and cobalt complexes of octadentate azamacrocycles: spectrophotometric titration, stopped-flow kinetics and crystallographic study.
abstract: Details of complex formation kinetics are reported for tetrakis(2-hydroxyethyl) substituted cyclen (L(1)) and cyclam (L(2)) with Cu(II) and Co(II). Stopped-flow kinetics and spectroscopic titration methods were employed for the activation parameters and stability constants, respectively. X-ray studies revealed that the pendant 2-hydroxyethyl groups are not equivalent: two are folded over the macrocycle and maintained by intramolecular hydrogen bonds while the others are extended and pointed away from the macrocyclic cavity. Complex formation kinetics and spectroscopic titration were performed in aqueous acidic buffer solutions. Thermodynamic and kinetic parameters revealed that the ring size of the macrocycles plays an extremely important role for each metal ion studied. Stopped-flow kinetic measurements explained the mechanism of the complex formation process of both Cu(II) and Co(II) which proceed in outer-sphere interactions with ligands. There are two steps in the complex formation of the system studied. The initial step is a second order reaction between the metal ion and macrocycle with a second order rate constant.
authors.affiliation: Onsekiz Mart University, Art and Science Faculty, Department of Chemistry, Canakklale, Turkey.
authors.forename: Hava
authors.initials: H
authors.lastname: Ozay
authors.forename: Yakup
authors.initials: Y
authors.lastname: Baran
authors.forename: Youichi
authors.initials: Y
authors.lastname: Ishii
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000080027:Cyclams; D006571:Heterocyclic Compounds / Q000737:chemistry; D007700:Kinetics; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008958:Models, Molecular; D013053:Spectrophotometry
chemical_list: D056831:Coordination Complexes; D000080027:Cyclams; D006571:Heterocyclic Compounds; D047028:Macrocyclic Compounds; C024560:cyclam; D003035:Cobalt; D003300:Copper; C038072:cyclen