Copper -, dimer

FIGURE 11.6 EPR of the copper dimer in pure copper acetate powder. Strong exchange coupling gives an S = 0 ground state and an S = 1 excited state at 2J 300 cm 1. At T = 48 K the triplet is hardly populated, and the spectrum is dominated by a trace of monomeric copper. 

Monovalent copper salts were initially found to be better catalyst precursors than divalent copper salts. The latter needed the addition of base. In the presence of dioxygen the copper(I) salts are oxidised to copper(II) hydroxides forming hydroxide bridged dimers. The hydroxides can be replaced by phenolates, thus producing the key-intermediate [23] (Figure 15.16). From this equilibrium we understand that water concentration should be kept low in order to have a maximum amount of phenoxides coordinated to the copper dimers. 

When two electrons are transferred from a phenoxide anion to the copper dimer, we form the phenoxonium cation and two copper(I) ions are formed. Most likely, the phenoxonium cations are not free in solution, but they are still coordinated to copper. The valence state cannot be rapidly deducted from the picture and thus we have indicated that below the respective complexes. A nucleophilic attack by another phenol (or phenoxide anion) takes place at carbon-4 of the phenoxonium ion (Figure 15.17). 

The X-ray diffraction crystal structure of another copper dimer showed a distance between ligand planes of 2.91 to 3.31 A, an intramolecular Cu-Cu distance of 6.01 A and an intermolecular Cu-Cu distance of 10.209 A.32 Calculation of the Cu-Cu distance based on the relative intensity of the half-field transition gave r = 5.88 A. 

Fig. 6.5. Crystal structures and H NMR spectra of a copper monomer (A) and the corresponding copper dimer (B). The signal assignment is also shown [22].

Figure 8 Dissociation of (a) glow discharge generated copper dimer ions using a filtered noise field results in (b) bare copper product ions.

Figure 1 Model of a hydroxide bridged copper dimer...

A similar molecular orbital analysis on the copper dimer system (Figure 1) was performed by Hay leading to... 

The Cn(l) H n(la) bridging angle is 95.0°, within the ferromagnetic range for hydroxy-bridged copper dimers (Section 2.8). Each dimeric nnit is linked to its neighbor by... 

The main factor which allows observation of the NMR signals is the rather small magnitude of hyperfine couplings involved. Small A values will not greatly affect the transverse relaxation time T2 of the proton [equation (18)] and thus the NMR bandwidth will not be greatly increased. Byers and Williams (56) have studied some dimeric cupric complexes which are models for copper dimer units in proteins. Interest was particularly centred around the possibility that, if appreciable copper(ii) interactions occur, a mechanism for mutual fast relaxation is provided which in turn may lead to much narrower linewidths and measurable paramagnetic shifts. The systems are illustrated in [6]. 

There was some broadening of the signal that was probably due to dipolar interactions. The CTB-Cu spectrum also exhibited a signal at higher field that was due to a Cu-Cu dimer complex similar to the structure found in copper acetate, Fig. 9c. No evidence of a copper formate-type dimeric structure. Fig. 9b, was found. Tha major difference in the ESR spectrum of the blend was the disappearance of the dimeric copper complex. Thia may be due to the formation of the transition metal complex. Since the copper dimer complex requires the association of four carboxylate endgroupa, association of the PSVP is likely to sterically hinder its formation. 

Copper Dimerization Diaryls from aryl halides s. 1, 660-2 Cu 2 ArHal Ar-Ar... 

An electrostatic mechanism with respeciation provides a reasonable explanation for the formation of the hydroxyl-bridged Cu dimer reported in the literature [28] in preparations with Cu ammines the tetraammine complex is electrostatically attracted to the silica surface, and when it approaches the surface it respeciates according to the local pH. The copper dimer species is more compact than monomeric Cu ammines, and so attains a higher Cu surface density. 

Figure 1 Copper dimer bridged by a ligand L. (a) ground state, (b) CT excited state. Relevant ligand and...

Zinc chloride/sodium chloride copper Dimerization of cyclic ketones... 

Figure 13 Examples of host-guest complexes (from top) Bell s torand, Heirtzler s copper dimer and Steed s podand.

An inorganic nanowire was synthesized by Mohwald et al by using arachidic acid and copper(II) sulfate. In the solid state, a copper dimer is known to coordi-... 

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