Copper complexes redox properties

Using a deprotonated hydroxyiminoamide ligand, Kruger and co-workers33 structurally characterized a discrete copper(III) compound (6). The square-planar structure is retained even in solution. Absorption and redox properties of this complex were also investigated. 

Comba and co-workers described a simple and efficient method for the determination of solution structures of weakly coupled binuclear copper(II) complexes.54 The technique involves the combination of molecular mechanics55,56 and EPR spectroscopy. From this standpoint they reported the structure of the complex (29). Using an acyclic tertiary tetraamine ligand, Bernhardt reported57 crystal structure of the complex (30), along with its redox properties. 

To better understand copper-dioxygen coordination chemistry with varying ligand type, Karlin and co-workers synthesized and investigated spectroscopic and redox properties of many complexes (218) (t= 1.005) and (219) (r = 0.19), (220) (t = 0.50),209 (221) (r = 0.19) and (222)... 

As a part of their work on copper(I)-dioxygen chemistry, Schindler and co-workers220 synthesized copper(I) (Section 6.6.4.2.2(iv)) and copper(II) complexes ((235) r = 0.12, and (236) r = 0.08) of a few tetradentate ligands, varying in their flexibility due to the presence of different chelate ring-forming arms, and studied their redox properties. Karlin and co-workers observed a... 

A few thioether-ligated copper(II) complexes have been reported, however (cf. Section 6.6.3.1.2) (417) (essentially square planar), (418) (two crystalline forms one TBP and other SP),361 (419) (SP),362 (420) (SP),362 (421) (TBP),362 (422) (SP),363 (423) (SP),363 (424) (two independent complexes SP and octahedral),364 (425) (TBP).364 In the complexes (420) and (421), EPR spectra revealed that the interaction between the unpaired electron and the nuclear spin of the halogen atom is dependent on the character of the ligand present. For (424) and (425), spectral and redox properties were also investigated. Rorabacher et al.365 nicely demonstrated the influence of coordination geometry upon CV/Cu1 redox potentials, and reported structures of complexes (426) and (427). Both the Cu1 (Section 6.6.4.5.1) and Cu11 complexes have virtual C3v symmetry. 

The copper(I) analogue [Cu(L)][C104] (744) (distorted tetrahedral) of copper(II) complex (201) was also synthesized and its redox property investigated.193 Structuresof complex (745) (distorted tetrahedral)557 and complex (746) (pseudotetrahedral Cu-Cu 4.764 A)558 were also reported. 

Copper(l) analogues [(L)Cu(MeCN)][CF3S03] (747) [yellow, four-coordinate (two amine donors, one of the two pyridinyl groups and an MeCN] and [(L)Cu(MeCN)][BF4] (748) [red, five-coordinate (two tertiary amine, two pyridinyl and an MeCN] [L as that in copper(II) complex (241)] were structurally characterized and redox properties of these complexes were also investigated.224... 

With the exception of Elder et. al., who used EXAFS to look at redox properties of copper complexes diffused in Nafion film modified electrodes (21), no in-situ studies have been reported on modified electrodes using EXAFS. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

The behavior of thiourea towards copper(II)-chloro complexes in acetone exemplifies the major changes in redox properties provoked by back-donation, as copper (I) and free chlorine are produced 50—52). The back-donation of copper(II) towards the sulfur atom of the thiourea ligand leads to a substantial decrease in electron population at the metal ion. Compensation is effected by the exercise of the EA function of copper towards coordinated chlorine until the electronic properties of copper and chloride approach those of copper (I) and chlorine (0) respectively ... 

The redox properties of the copper(II) ion in saturated polyaza macrocyclic complexes CuN4 and CuNj have been shown1020 to vary with the chelate ring size, and the very negative E° values (Figure 62) are consistent with a macrocyclic effect , from stability constant measurements.976... 

The redox properties of dinuclear copper(II) complexes have received extensive attention using cyclic voltammetry measurements, and it was recognized in the early literature that the two copper(II) ions could be reduced to copper(I) at the same potential or at different potentials (Section 53.3.7).30,934,1021,1022 In either case the reduction requires a two electron process and if the E° values are well separated may result in the observation, under favourable circumstances, of a two-peaked cyclic voltammogram (Figure 61b), as in... 

Reaction of Cytochrome cIinn with Bis(ferrozine)copper(II) Knowledge of the redox properties of cytochrome c was an encouragement to initiate a kinetics investigation of the reduction of an unusual copper(II) complex species by cyt c11. Ferrozine (5,6-bis(4-sulphonatophenyl)-3-(2-pyridyl)-1,2.4-triazine)286 (see Scheme 7.1), a ligand that had come to prominence as a sensitive spectrophotometric probe for the presence of aqua-Fe(II),19c,287 forms a bis complex with Cu(II) that is square pyramidal, with a water molecule in a fifth axial position, whereas the bis-ferrozine complex of Cu(I) is tetrahedral.286 These geometries are based primarily upon analysis of the UV/visible spectrum. Both complexes are anionic, as for the tris-oxalato complex of cobalt in reaction with cytochrome c (Section 7.3.3.4), the expectation is that the two partners will bind sufficiently strongly in the precursor complex to allow separation of the precursor formation constant from the electron transfer rate constant, from the empirical kinetic data. 

The free radical-copper complex in active GAOX combines two distinct reactive sites to form a two-electron redox unit in the protein with new properties, different from those of the individual components. The... 

Macrocyclic polythioethers form coordination compounds with many transition metal ions [55] and, owing to their moderate rr-acidity (intermediate between that of amines and phosphines), can exert a stabilizing effect on lower oxidation states of the encircled metal [56]. Copper complexes of thiacrowns have been widely investigated, even in view of the fact that they can be considered convenient models in the study of redox properties of cuproproteins (systems whose active site is a copper center bound to the thioether groups of methionine residues [57]). 

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