Copper divalent state

Several copper minerals, containing copper in the divalent state, are completely soluble in sulfuric acid according to the following reactions ... 

CuO, the mineral tenorite, and AgO are well known but their structures are quite different. More importantly the valence states in these two compounds are quite different. In CuO, the copper is formally in the divalent state, whereas in AgO, there exist two types of silver atoms, one in formal oxidation state 1+, the other in 3+. These two silver ions also possess strong covalent character. PdO and CuO, however, have similar crystal structures based on chains of opposite edged-shared, square-planar M04 groups. 

Cupric. Pertaining to copper combined in the divalent state or in the form of the doubly charged ion Cu++. 

Copper complexes are known in oxidation states ranging from 0 to +4, although the +2 (cupric) and the +1 (cuprous) oxidation states are by far the most common, with the divalent state predominating. Only a relatively small number of Cu complexes have been characterized and the Cu° and oxidation states are extremely rare. A few mixed valence (see Mixed Valence Compounds) polynuclear species have also been isolated examples include a CuVCu species and a Cu /Cu catenane. The coordination numbers and geometries (see Coordination Numbers Geometries) of copper complexes vary with oxidation state. Thus, the majority of the characterized Cu complexes are square planar and diamagnetic, as is common for late transition metals with d electronic configurations. 

It is noteworthy that oxidation of 11+ to the divalent copper(II) state affords exclusively the 5-coordinate species after rearrangement of the system. The bis-terpy complex, which would be formed by decomplexation of the copper(II) center and recoordination to the terpy fragments of two different molecules of 12, is not detected. This observation is important in relation with the general mechanism of the changeover step converting a 4-coordinate Cu(II) species [Cu(II)(4)] into the corresponding stable 5-coordinate complex... 

The copper center. Galactose oxidase is capable of catalyzing a two-electron reduction, although it only contains a single type 2 copper center. This assumption is, however, incorrect. Recent studies show that the copper ion occurs in its divalent state, Cu2+, which is antiferromagnetically coupled to a tyrosyl radical (Tyr272) and is, therefore, ESR-inactive [158]. 

One biological pair that has been studied is that comprising cytochrome c [cyt(II)] with its heme iron in a divalent state, and plastocyanin [pc(II)] with its blue copper center also in a divalent state. " Because cyt(II) is positively charged and pc(II) is negatively charged, an encounter complex is obtained prior to electron transfer to give cyt(III) and pc(I)... 

Plastocyanin is a copper-containing protein. The reversible transition of copper between the monovalent and divalent states is responsible for its reducing and oxidizing character respectively. 

In other work, a diethyldithiocarbamate copper(II)-loaded zeolite has been prepared and characterized by a range of techniques (1793). However, only a small fraction of the copper ions bind the dithiocarbamate, probably those on the surface, as the large diethyldithiocarbamate anion cannot easily pass through the windows or pore openings of the channels into the cavities of the zeolite. The precise binding mode of the dithiocarbamate remains unknown, although ESR data show that the copper is still in the divalent state. 

Solvation of the divalent copper ion requires some special remarks. In solid state hexa-coordinate Cu2+ shows Jahn-Teller distortion the metal-ligand bonds of four ligands in the equatorial plane are shorter... 

The initial question was whether the active catalyst is copper metal, copper(I), or copper(II), because all metal precursors gave results. Without the proper control of the valence state and the ligand environment the selectivities for the copper catalysed cyclopropanations (or carbene insertion reactions) have remained low or inconsistent for a long period of time. It was only in the sixties that a more systematic study of these issues was started. Several divalent copper salts were successfully used, but Kochi and Salomon [1] showed with the use of Cu(I)OTf that most likely copper(I) was the actual species needed for this reaction. 

Cobalt and nickel are Group VlllA and copper Group IB elements. They occur predominantly in the +2 oxidation state in soils as divalent cations, though Co + may be oxidized to Co forming very insoluble compounds with Mn oxides, and... 

The Cupric, Cu2+ or Cu(II) State, 3d9 The most important and stable oxidation state for copper is divalent. There is a well-defined aqueous chemistry of the Cu2+ ion, which generates the familiar blue solution when complexed with water. A large number of copper coordination compounds exist and these have been studied extensively. A strong Jahn-Teller distortion is associated with the 3d9 electronic configuration of this ion. This implies that a regular tetrahedron or octahedron about the Cu2+ ion is never observed, except in the rare occurrence of a dynamic Jahn-Teller effect. The tetragonal distortion about an octahedron can lead to a square-planar coordination which is often observed in Cu(II) oxides. 

The high affinity shown by carboxylic acids for copper (II) compared with the remaining divalent metals of the first transition series appears to be due in part to the stabilization of the extracted complexes by the formation of the well-known dimeric structure (1) in which copper(II) carbox-ylates exist in the solid state and in non-donor solvents.54 The axial ligands, L, consist of undissociated carboxylic acid molecules55 or, in the absence of an excess amount of extractant, they may consist of water or other solvent molecules.56 Copper was successfully removed from nickel sulfate solutions on the base-metal plant at Matthey Rustenburg Refiners in South Africa by being extracted into Versatic 10 acid at a controlled pH value. The process is believed to have been discontinued only because improvements in the selective leaching of copper and nickel rendered it unnecessary. 

The Cr A and several other zeolites containing transition metal ions, which may exist in two or more valence states, were also found to be oxidation catalysts. One such system of note is the copper containing Type Y zeolite, the redox chemistry of which was studied in several recent investigations (2, 3.4, 5). These studies established the range of conditions at which copper exists in divalent, monovalent, or zerovalent state and in particular determined the reduction conditions in hydrogen and carbon monoxide atmospheres for a complete conversion of Cu Y to Cu Y but no further to Cu°. The Cu ions in type Y zeolite were reported to be specific adsorption centers for carbon monoxide ( 6), ethylene ( 7), and to catalyze the oxidation of CO (8). In the present work the Cu ions were also found to be specific adsorption centers for oxygen. 

The /wentfo-macrocyclic structure is also present in the solid state forms of some free ligands. [62] Overall, these are less planar than their 4-coordinate metal complexes, having a step conformation to reduce the repulsion between the central phenolic protons. Nevertheless, they are apparently well organized for complex formation and donor cavity sizes [63] give a good fit for divalent copper. [62]... 

The composition of the complexes above depends on the metal nature and its oxidation state. Thus, divalent copper, zinc, and cadmium form complexes of the type 811a (L = py, bipy, 1,10-phen m= 1, 2) [605], tetravalent tin forms chelates 811b (X — S [606], Se [607]). The electrochemical cleavage of the S — S bond is observed not only in ligands with aromatic bridge 810, but also in those with aliphatic one, for example (CH2) in 812 [608] ... 

Reduction of the copper(II) halides to copper(I) halides may be carried out using sulfite or copper metal. If the reduction with copper metal is carried out in concentrated HC1 solution, the solution takes on an intermediate black color before fading to the colorless CuCl ion. The black color is probably due to dimeric or polymeric ions having copper in both the +1 and +2 states, for example, Cl—Cu—Cl—CuC12(H20) . The reduction of divalent copper by cyanide to form the cyano complex, Cu(CN)73, was mentioned in Chapter 10, and the reaction between cupric and iodide ions is similar to this, releasing iodine and forming the very insoluble copper iodide ... 

---