Cuprates are a class of compounds that contain copper (Cu) atom(s) in an anion. The term 'cuprate' itself originates from 'cuprum', the Latin word for copper. Cuprates appear mainly in three contexts: anionic organocopper species; inorganic, anionic coordination complexes; and complex oxides.
Organic cuprates typically have a formula, corresponding to a copper(I) oxidation state, where at least one of the R groups can be any organic group. These compounds are frequently used in organic synthesis as weak nucleophiles that preferentially attack π bonds. An example of an organic cuprate is dimethylcuprate(I) anion .
Inorganic cuprate complexes have a wide variety of formulas. An inorganic cuprate example is the tetrachloridocuprate(II) or tetrachlorocuprate(II) () anion, a copper(II) atom coordinated to four chloride ions.
Cuprate oxide salts are layered materials with general formula , and some are non-stoichiometric. Many of these compounds are known for their superconducting properties.
Oxide cuprates
thumb|Potassium cuprate
Many stable or metastable alkali metal cuprates(III) are known, all salts of the polyanion . They are strong oxidants, oxidizing water. but sodium cuprate(III) is red-brown.
One of the simplest oxide-based cuprates is potassium cuprate(III) . Even so, is a non-stoichiometric compound, so the more exact formula is and x is very close to 2. This causes the formation of defects in the crystal structure, and this leads to the tendency of this compound to be reduced. Cyanide gives analogous complexes but also the trianionic tetracyanocuprate(I), . Dicyanocuprate(I), , exists in both molecular or polymeric motifs, depending on the countercation.
Copper(II)
thumb|upright|right|Caesium salt of hexafluorocuprate(IV)
Cuprates containing copper(II) include trichlorocuprate(II), , which is dimeric, and square-planar tetrachlorocuprate(II), , and pentachlorocuprate(II), . 3-Coordinate chlorocuprate(II) complexes are rare.
Tetrachlorocuprate(II) complexes tend to adopt flattened tetrahedral geometry with orange colors.
Sodium tetrahydroxycuprate(II) () is an example of a homoleptic (all ligands being the same) hydroxide complex.
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Copper(III) and copper(IV)
Hexafluorocuprate(III) and hexafluorocuprate(IV) are rare examples of copper(III) and copper(IV) complexes. They are strong oxidizing agents.
Organic cuprates
thumb|upright|Structure of lithium diphenylcuprate(I) etherate, .
Cuprates have a role in organic synthesis. They are invariably Cu(I), although Cu(II) or even Cu(III) intermediates are invoked in some chemical reactions. Organic cuprates often have the idealized formulas and , both of which contain copper in an oxidation state of +1, where R is an alkyl or aryl. These reagents find use as nucleophilic alkylating reagents.
See also
- Cuprate superconductor
- High-temperature superconductivity
- Gilman reagent