Journal article

Authors list: Schindler, S; Elias, H; Paulus, H

Publication year: 1990

Pages: 607-618

Journal: A Journal of Chemical Sciences

Volume number: 45

Issue number: 5

ISSN: 0932-0776

DOI Link: https://doi.org/10.1515/znb-1990-0507

Publisher: De Gruyter

Abstract: 

A series of binuclear, hydroxyl-bridged copper(II) complexes 1-10 with the general formula [Cu₂(LR₂D₂)(OH)](ClO₄)₂ was prepared and characterized. The mono basic, five- or sevendentate ligands HLR₂D₂
were obtained either by reduction of the Schiff bases derived from the
condensation of 2,6-diformyl-4-methylphenol and the amines H₂N – D (complex 1: D = -(CH₂)₂-NH₂; 2: -(CH₂)₂-NMe₂; 3: -(CH₂)₂-NEt₂; 4: -(CH₂)₃-NEt₂; 5: -(CH₂)₂-4-imidazolyl; 6: -CH₂-2-pyridyl; 7: -(CH₂)₂-2-pyridyl)
or by reacting 2,6-di-(chloromethyl)-4-methylphenol with
2-[(2-methylamino)ethyl]pyridine (complex 8),
Ν,Ν,N′,N′-tetraethyldiethylenetriamine (complex 9) or
bis[2-(2-pyridyl)ethyl]amine (complex 10) under HC1 elimination. The
UV/VIS spectra of complexes 1-8 with two four-coordinate copper centers
and of 9 and 10 with two five-coordinate copper centers are discussed.
An X-ray structure analysis of complex 6 (= [Cu₂(LR₂D₂)(OH)](ClO₄)₂ with R = H and D = -CH₂-2-pyridyl)
was carried out. 6 crystallizes in the orthorhombic space group Pbca
and the two copper centers have practically co-planar, doubly O-bridged
cis-N₂O₂ coordination geometries with one
perchlorate anion being weakly coordinated to each copper. Stopped-flow
spectrophotometry was used to study the kinetics of copper removal from
[Cu₂(LR₂D₂)(OH)]²⁺ with EDTA in the pH range 8.5-6.6 at 20 °C and I = 0.2 M (NaClO₄). The reaction is first-order in both complex and EDTA, the rate law being: rate = k[complex][EDTA]_total. At pH 8.0 second-order rate constants k range from 40.3 x 10³ M ^-1s^-1 (complex 6) to 3.72x 10^-2 M^-1s^-1 (complex 9). It follows from the pH dependence of k that both species H₂EDTA^2- and HEDTA^3- react independently with [Cu₂(LR₂D₂)(OH)]²+, the reactivity of H₂EDTA^2- being considerably greater than that of HEDTA^3-.
The experimental facts support the operation of an associative (A)
mechanism with the removal of the first copper being rate-controlling.
The kinetic effects of the donor group D and substituent R are
attributed to steric and/or electronic interactions.

Harvard Citation style: Schindler, S., Elias, H. and Paulus, H. (1990) Kinetics and Mechanism of Ligand Substitution in Binuclear Copper(II) Complexes as Model Compounds for Hemocyanin, Zeitschrift fur Naturforschung B, 45(5), pp. 607-618. https://doi.org/10.1515/znb-1990-0507

APA Citation style: Schindler, S., Elias, H., & Paulus, H. (1990). Kinetics and Mechanism of Ligand Substitution in Binuclear Copper(II) Complexes as Model Compounds for Hemocyanin. Zeitschrift fur Naturforschung B. 45(5), 607-618. https://doi.org/10.1515/znb-1990-0507