Copper mixed oxidation states

An interesting phenomenon is the occurrence of dithiocarbamates with copper in mixed oxidation states. 

In many complexes, mixed oxidation states for the transition metals are found. Complex (41) is a diamagnetic compound with the actual composition (42).68 Copper dithiocarbamates are synthesized not only with copper in the oxidation states I, II or III but also with the metal in mixed oxidation states III and I (43, 44, 45), II and I (46, 47) and even III and I [48, 49).56 Complex (50), which has two isomeric structures a and / , has Ru either in a trapped oxidation state II,in or in a delocalized oxidation state of 2.5. The /J-isomer is the most stable.69 Slow, controlled potential electrochemical oxidation of (51) yields (52), in which the metal has a trapped oxidation state II,HI.70... 

Copper-containing high-temperature superconductors contain mixed oxidation states of Cu. Thus, once the Cu oxidation states are worked out for each complex oxide given, all except Gd2Ba2Ti2Cu20n (compound c), which contains only Cu are superconductors. The average oxidation state of copper in compound (a) is +2.25, in (b)... 

The theoretical interpretation of the high temperature superconductors is still under development. The copper oxide ceramic superconductors obtain their paired conducting electrons from copper in mixed oxidation states of I and II or II and III, depending on the particular system. The paired conducting electrons are called Cooper pairs, after Leon N. Cooper. Cooper s name also gives us the C of BCS the BCS theory is an interpretation of superconductivity for low temperature superconductors (having Tc s of less than 40 K). 

Soda. Ash Roasting. Some of the first processes to recover selenium on a commercial basis were based on roasting of copper slimes with soda ash to convert both selenium and tellurium to the +6 oxidation state. Eigure 1 shows flow sheets for two such processes. Slimes are intensively mixed with sodium carbonate, a binder such as bentonite, and water to form a stiff paste. The paste is extmded or peUetized and allowed to dry. Care in the preparation of the extmdates or pellets is required to ensure that they have sufficient porosity to allow adequate access to the air required for oxidation. 

Assigning oxidation states of —2 to oxygen, + 3 to yttrium and + 2 to barium, one would obtain an oxidation state 7/3 for copper when jc = 0. The non-integer oxidation state of copper is interpreted as if 2/3 of the ions are present as Cu2+ and 1/3 as Cu3 +. This mixed-valent composition seems to be determinant for the occurrence of superconductivity. In fact, as noted in Table 1, all the superconducting ceramic oxides contain Cu in a non-stoichiometric composition. 

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