Copper complexes electronic properties

The stereochemistry and electronic properties of fluxional six-coordinate copper(II) complexes. B. Hathaway, M. Duggan, A. Murphy, J. Mullane, C. Power, A. Walsh and B. Walsh, Coord. Chem. Rev., 1981,36, 267-324 (132). 

The discussion above might have pertained for example, to the energies and electronic spectra of titanium(iii) compounds. The same ideas can be applied with just one modification to the i/-electron properties of copper(ii) complexes and other... 

Several copper enzymes will be discussed in detail in subsequent sections of this chapter. Information about major classes of copper enzymes, most of which will not be discussed, is collected in Table 5.1 as adapted from Chapter 14 of reference 49. Table 1 of reference 4 describes additional copper proteins such as the blue copper electron transfer proteins stellacyanin, amicyanin, auracyanin, rusticyanin, and so on. Nitrite reductase contains both normal and blue copper enzymes and facilitates the important biological reaction NO) — NO. Solomon s Chemical Reviews article4 contains extensive information on ligand field theory in relation to ground-state electronic properties of copper complexes and the application of... 

EPR. The EPR of the Cu complex 62c has been reported as a 1% powder sample at 77 K and is given in Table XI (Section IV.A), which compares the EPR data for 62c to Cu[pz(SMe)8] (48) (Scheme 9), Cu(TPP) and Cu(pc). The spectrum is typical of a monomeric square-planar copper with axial symmetry. The EPR spectrum for 62c closely matches that of 48 implying that although the peripheral tridentate coordination geometry has an effect on the ir-clcctronic structure of the pz ring it does not effect the electronic properties of the central Cu2+ ion, whose unpaired electron density is in a a orbital. 

Hathaway has attempted to assess the value of the electronic properties of polycrystalline mononuclear copper complexes with the [CUN4], [CuNj], and [CuN ] chromophores of unknown crystal structure, in predicting the stereochemical environment of the copper(ii) atom. The value of having B. J. Hathaway, J.C.5. Dalton, 1972, 1196. 

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 ... 

This review of mixed valence copper(I)/(II) systems has clearly established the predominance of the class I Robin and Day behaviour (Table 17), 360-362 but equally has shown how few copper class II or III systems have been well defined. This particularly applies to the class II systems, which can still be considered well-defined coordination complexes, with the electronic properties of these systems in the solid state and in solution. This suggests a fruitful area of research in these copper(I)/(II) mixed valence systems, especially of class II behaviour. 

The following sections (53.4.4.2-6) attempt to describe the electronic properties of simple mononuclear complexes of the copper(II) ion,47,48 to show how these are related to the different stereochemistries of the copper(II) ion and how these properties are modified by the formation of polynuclear complexes.17,30 Particular emphasis is placed on the appearance of the different types of electronic property and how they may be used to provide qualitative evidence for the different types of copper-copper interactions, and hence for possible polynuclear structure formation, particularly in the solid state. While the main emphasis will be on the electronic properties in the solid state, where X-ray evidence may be obtained for a single magnetic species,10 the measurement of the electronic properties in solution will also be described, although in solution a mixture of complex species may be present in equilibrium and complicate the interpretation of the electronic properties.584,816,817,824... 

At the end of this section on the relationship between the electronic properties and the stereochemistry of complexes of the copper(II) ion, it is worth summarizing the most useful physical techniques which offer a criterion for the presence of a polynuclear copper(II) complex rather than a mononuclear complex. These are (i) magnetic susceptibility measurements down to near absolute zero, for the determination of O or / values (ii) ESR spectra of magnetically dilute systems, in the solid state or in solution, to obtain hyperfine data and (iii) cyclic voltammetry to show evidence for a one-step reduction process in a Cu2 species. 

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