Applicability of the Marcus relationship to copper(II/I) electron transfer. Comparison of NMR self-exchange relaxation and reduction and oxidation cross-reaction kinetics for a macrocyclic amino tetrathiaether-copper(II/I) complex in aqueous solution

Electron Transfer by Copper Centers

“…Vande Linde et al 151 studied the electrontransfer kinetics of a Cu(II/I) system involving a 15-membered macrocyclic ligand containing four thiaether sulfurs and one amine nitrogen ( [15]aneNS 4 , Figure 11). This system exchanged electrons very rapidly and, therefore, is treated in the section on rapidly reacting systems below.…”

“…A closely related ligand, designated as [15]aneNS 4 ( Figure 11), in which one of the sulfur donor atoms was replaced by an amine nitrogen donor atom, yielded k 11 ) (1-2) × 10 5 M -1 s -1 by NMR, and this value was shown to be consistent with k 11 values generated from both Cu II L reduction and Cu I L oxidation reactions. 151 The Cu II/I ([13]aneS 4 ) system, which was cited earlier with the macrocyclic polythiaether complexes, also yielded a large k 11 value of 3 × 10 5 M -1 s -1 as determined by NMR with corroborative k 11 values being generated from reduction reactions of Cu II L. 133 An examination of the crystal structures shows that this system is structurally similar to the Cu II/I ([15]aneS 5 ) system in that both Cu II ( [15]aneS 5 ) 169 and Cu II ( [13]aneS 4 ) 170 are square pyramidal, the latter having a water molecule occupying the apical site. Upon reduction of the former complex, one of the Cu-S bonds in the plane dissociates to generate a tetrahedral complex in which none of the donor atoms is required to change the orientation of its lone electron pair.…”

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

“…However, when the energy required for the geometric change from the tetrahedral to the tetragonal structure is not large, such gated behavior diminishes and the Marcus cross relation is successfully applied to the estimation of the self-exchange rate constant. 9 Early works on the outer-sphere reactions of copper cpmplexes centered on reactions of Cu(bpy) 2 2+/+ , Cu(phen) 2 2+/+ , and its derivative Cu(dmp) 2 2+/+ . [10][11][12] In 1983, Lee and Anson pointed out that the steric interconversion may have an important role in the electron-transfer processes of the Cu(bpy) 2 2+/+ and Cu(phen) 2 2+/+ couples.…”

Comparative study of donor atom effects on the thermodynamic and electron-transfer kinetic properties of copper(ii/i) complexes with sexadentate macrocyclic ligands. [CuII/I([18]aneS4N2)] and [CuII/I([18]aneS4O2)]

“…For all three sexadentate macrocyclic systems, the k 11 values are one to two orders of magnitude smaller than the values reported previously for the related quinquedentate systems, [Cu II/I ([15]aneS 4 )] 2+/+ 4 and [Cu II/I ([15]aneNS 4 )] 2+/+ . 17 In these five-coordinate systems, a single Cu-S bond ruptures upon reduction and the remaining four coordinate bonds are prearranged in a more nearly tetrahedral array, which presumably diminishes the reorganizational energy. Thus, although the [18]aneS 6 , [18]aneS 4 O 2 and [18]aneS 4 N 2 systems avoid the rupture of copper-solvent bonds, their reorganization energies are significantly affected relative to the smaller five-coordinate macrocyclic systems.…”

“…Previous investigations in our laboratory have examined the various thermodynamic and kinetic properties of a variety of Cu(II/I) complexes formed with macrocyclic polythioethers 1-14 and mixed donor ligands [15][16][17][18] with a specific focus on understanding the effect of conformational constraints on the electron-transfer kinetic behavior. The majority of these studies has involved complexes formed with tetrathioether ligands with variable geometric constraints imposed either by substituted peripheral groups or alterations in the ring size.…”