Chloro-copper complexes

An extensive literature exists on the characterization and structure—activity correlation of industrial copper-alumina oxychlorination catalysts [95-120]. At least two different major copper species have been identified. At low concentrations of copper (below ca 5 %), a well-dispersed copper species in intimate interaction with the alumina surface is formed. This species has a very low oxychlorination activity. At higher concentrations, a second species, probably formed by the de-position/precipitation of the copper chloro complexes, is observed. The latter gives rise to the active sites during the oxychlorination reaction. On the basis of an FTIR study of the oxychlorination reaction Finocchio et al. [42] postulated the formation of surface copper chloride-ethylene r-complex intermediates (which lead eventually to EDC) and weakly adsorbed HCl during oxychlorination. Formate species associated with copper and probable precursors for formation of the oxides of carbon by combustion were also identified. 

The anhydrous chloride is prepared by standard methods. It is readily soluble in water to give a blue-green solution from which the blue hydrated salt CuClj. 2H2O can be crystallised here, two water molecules replace two of the planar chlorine ligands in the structure given above. Addition of dilute hydrochloric acid to copper(II) hydroxide or carbonate also gives a blue-green solution of the chloride CuClj but addition of concentrated hydrochloric acid (or any source of chloride ion) produces a yellow solution due to formation of chloro-copper(ll) complexes (see below). 

Nickel and Cobalt. Often present with copper in sulfuric acid leach Hquors are nickel [7440-02-0] and cobalt [7440-48-4]. Extraction using an organophosphoric acid such as D2EHPA at a moderate (3 to 4) pH can readily take out the nickel and cobalt together, leaving the copper in the aqueous phase, but the cobalt—nickel separation is more difficult (274). In the case of chloride leach Hquors, separation of cobalt from nickel is inherently simpler because cobalt, unlike nickel, has a strong tendency to form anionic chloro-complexes. Thus cobalt can be separated by amine extractants, provided the chloride content of the aqueous phase is carefully controUed. A successhil example of this approach is the Falcon-bridge process developed in Norway (274). 

In contradistinction to this, weak ferromagnetism has been observed in a number of chloro and bromo complexes of the type M2[CrX4] (M = a variety of protonated amines and alkali metal cations, X = Cl, Br), which are analogous to previously known copper(II) complexes (p. 1192). They have magnetic moments at room temperature in the region of 6BM (compared... 

An even more serious problem can arise when dissolved species expected to predominate at high temperatures are undetectable at 25°C or are only present at concentrations which are too low for them to be adequately characterized thermodynamically. Examples are certain transition metal chloro-complexes (9,10) and mixed complexes of such metals with hydroxide and another ligand (11,12). Thus it seems that chloride complexing so alters the aqueous chemistry of copper and gold that supposedly inert gold components in autoclaves are reversibly oxidized by Cull (10) and it is likely that mixed oxine and hydroxy complexes of Fell contribute considerably to the gross under-estimation (by a factor of up to 10 ) of magnetite solubility in oxine (12,14). 

Primary separation occurs in the leaching procedure, where the metals copper, zinc, and nickel are dissolved as metal ammonium chlorides or chloro complexes, while iron and chromium remain in the solid residue as hydroxides. 

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 ... 

Chloro(isocyanato)copper(I) complexes, liquid crystals,... 

Several complexes have beeai found to be dimeric. Infrared spectroscopy shows that the CuNCS(L) complexes (L = py, 2- or 4-picoline, 3,5-lutidine, or quinoline) contain bridging thiocyanato groups (332). The mass spectra of CuX P(cyclohexyl)3 complexes (X = Cl, Br, I) show no peaks of higher mass than those corresponding to dimeric molecules, and the far-infrared spectrum of the chloro complex indicates that they are dimeric with halo bridges (248). Triphenylphosphine reacts with copper(I) trifluoroacetate in dichloromethane to give [Cu(02C CF3)(PPh3)]2 which is dimeric in chloroform but partially dissociated in dichlorobenzene (107). 

The bulky ligand tri (cyclohexyl )phosphine reduced copper(II) chloride or bromide in ethanolic solution to CuX P(CeHii)3 2 (X = Cl, Br) complexes. The far-infrared spectrum of the chloro complex indicated that it contained terminal chloride, and the molecular weights of these complexes in solution are consistent with a monomeric formulation (248). Similarly, the molecular weight of CuCl(SbPh3)2—obtained by fusion of the ligand with CuCl— in benzene shows it to be monomeric (329). 

Keywords poly(dihalophenylene oxide), bis (4-chloro-2,6-dibromo phenoxo) ethylenediamine copper (II) complex... 

The method of frontal analysis on an ion-exchange column was used to study the formation of weak chloro complexes of nickel(II), cobalt(II) and copper(II). Although, the reported dissociation constant for the complex NiCr (X iss = (4.6 0.1), which can be converted to log,) X, = - (0.66 0.01)) is close to other reported values, some experimental data, such as the temperature of the measurements, were not published. Therefore, the reported constant is rejected in this review. 

BJE/SKI] Bjerrum, J., Skibsted, L. H., Weak chloro complex formation by copper(ll) in aqueous chloride solution, Inorg. Chem., 25, (1986), 2479-2481. Cited on page 413. 

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