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{{Short description|Metallic compound with anionic copper complexes}}
{{for|cuprate superconductors|Cuprate superconductor}}

{{Use American English|date=January 2019}}
{{Use mdy dates|date=January 2019}}

'''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 complex]]es; and [[complex oxide]]s.{{cn|date=January 2024}}

Organic cuprates typically have a {{chem2|[CuR2]−}} formula, corresponding to a copper(I) [[oxidation state]], where at least one of the R groups can be any [[Organic compound|organic group]]. These compounds are frequently used in [[organic synthesis]] as weak [[nucleophile]]s that preferentially attack [[π bond]]s.{{cn|date=January 2024}} An example of an organic cuprate is dimethylcuprate(I) anion {{chem2|[Cu([[methyl|CH3]])2]-}}.

Inorganic cuprate complexes have a wide variety of formulas.  An inorganic cuprate example is the tetrachloridocuprate(II) or tetrachlorocuprate(II) ({{chem2|[CuCl4](2-)|auto=1}}) [[anion]], a copper(II) atom coordinated to four [[chloride]] ions.

Cuprate oxide salts are [[layered material]]s with general formula {{chem2|XYCu_{''m''}O_{''n''}|}}, and some are non-stoichiometric. Many of these compounds are known for their [[superconductivity|superconducting]] properties.{{cn|date=January 2024}} 

==Oxide cuprates==
[[File:Potassium cuperate.png|thumb|Potassium cuprate]]
Many stable or metastable [[alkali metal cuprates(III)]] are known, all salts of the polyanion {{chem2|[CuO2−]_{''n''}|}}.  They are strong [[oxidants]], oxidizing water.<ref name="cjc" />  They are typically produced through extremely large oxygen [[Thermodynamic activity|activities]].  Alkali metals larger than [[sodium]] produce dark-blue salts,<ref name=BHandbk/><ref name="TA">{{cite journal |last1=Costa |first1=Giorgio A. |last2=Kaiser |first2=Elena |title=Structural and thermal properties of the alkaline cuprate KCuO<sub>2</sub> |journal=Thermochimica Acta |date=1995 |volume=269-270 |pages=591–598 |doi=10.1016/0040-6031(95)02575-8 |url=https://www.sciencedirect.com/science/article/abs/pii/0040603195025758 |access-date=20 January 2023|url-access=subscription }}</ref> but sodium cuprate(III) is red-brown.<ref name="cjc">{{cite journal |last1=Magee |first1=J. S. |last2=Wood |first2=R. H. |title=Studies of Sodium Cuprate(III) Stability |journal=Canadian Journal of Chemistry |date=1965 |volume=43 |issue=5 |pages=1234–1237 |doi=10.1139/v65-164 |doi-access=}}</ref>

One of the simplest oxide-based cuprates is potassium cuprate(III) {{chem2|KCuO2}}.<ref name=BHandbk>{{cite book|chapter=Potassium Cuprate (III)|title=Handbook of Preparative Inorganic Chemistry|edition=2nd|editor=G. Brauer|publisher=Academic Press|year=1963|location=NY|volume=2|page=1015}}</ref>  Even so, {{chem2|KCuO2}} is a [[non-stoichiometric]] compound, so the more exact formula is {{chem2|KCuO_{''x''}|}} and ''x'' is very close to 2. This causes the formation of [[Crystallographic defect|defects in the crystal structure]], and this leads to the tendency of this compound to be [[Redox|reduced]].<ref name="TA" />

One of the most studied inorganic cuprates is {{chem2|YBa2Cu3O7|auto=1}}, also known as [[Yttrium barium copper oxide|YBCO]]. This [[oxide]] cuprate has been the subject of extensive research due to its ability to [[High-temperature superconductivity|conduct electricity without resistance at relatively high temperatures]].  It is the parent of a family of [[cuprate superconductor]]s.{{cn|date=January 2024}}

==Coordination complexes==
Copper forms many anionic [[coordination complex]]es with negatively charged ligands such as cyanide, hydroxide, and halides, as well as alkyls and aryls (see {{slink||Organic cuprates}}).
 
===Copper(I)===
Cuprates containing copper(I) tend to be colorless, reflecting their [[Electron configuration|d<sup>10</sup> configuration]]. Structures range from [[linear molecular geometry|linear]] [[Coordination number|2-coordinate]], [[trigonal planar]], and [[tetrahedral molecular geometry]]. Examples include linear {{chem2|[Cu[[Chloride|Cl]]2]−}} and trigonal planar {{chem2|[CuCl3](2−)}}.<ref>{{cite journal |doi=10.1039/c003948a |title=Cu(I)/(II) based catalytic ionic liquids, their metallo-laminate solid state structures and catalytic activities in oxidative methanol carbonylation |year=2010 |last1=Stricker |first1=Marion |last2=Linder |first2=Thomas |last3=Oelkers |first3=Benjamin |last4=Sundermeyer |first4=Jörg |journal=Green Chemistry |volume=12 |issue=9 |page=1589}}</ref> [[Cyanide]] gives analogous complexes but also the trianionic tetracyanocuprate(I), {{chem2|[Cu([[Cyanide|CN]])4](3−)}}.<ref>{{Cite journal |doi=10.1139/v99-181 |title=A multinuclear magnetic resonance study of crystalline tripotassium tetracyanocuprate |year=1999 |last1=Kroeker |first1=Scott |last2=Wasylishen |first2=Roderick E. |journal=Canadian Journal of Chemistry |volume=77 |issue=11 |pages=1962–1972}}</ref> Dicyanocuprate(I), {{chem2|[Cu(CN)2]−}}, exists in both [[molecular]] or [[polymeric]] motifs, depending on the [[Counterion|countercation]].<ref>{{cite journal |doi=10.1021/ic000399s |title=Crystal Structures and Vibrational Spectroscopy of [NBu<sub>4</sub>][Cu(CN)X] (X = Br, I) and [NBu<sub>4</sub>][Cu<sub>3</sub>(CN)4]·CH<sub>3</sub>CN |year=2000 |last1=Bowmaker |first1=Graham A. |last2=Hartl |first2=Hans |last3=Urban |first3=Victoria |journal=Inorganic Chemistry |volume=39 |issue=20 |pages=4548–4554}}</ref>

===Copper(II)===
[[File:CCs2CuF6.svg|thumb|upright|right|Caesium salt of hexafluorocuprate(IV)]]
Cuprates containing copper(II) include trichlorocuprate(II), {{chem2|[CuCl3]−}}, which is dimeric, and [[square-planar]] tetrachlorocuprate(II), {{chem2|[CuCl4](2−)}}, and pentachlorocuprate(II), {{chem2|[CuCl5](3−)}}.<ref name="Greenwood&Earnshaw2nd">{{Greenwood&Earnshaw2nd}}</ref><ref>{{cite journal |doi=10.1016/j.poly.2006.01.005|title=Two Halide Exchange in Copper(II) Halide Dimers: (4,4{{prime}}-Bipyridinium)Cu<sub>2</sub>Cl<sub>6−''x''</sub> ''BRX'' |year=2006 |last1=Willett |first1=Roger D. |last2=Butcher |first2=Robert E. |last3=Landee |first3=Christopher P. |last4=Twamley |first4=Brendan |journal=Polyhedron |volume=25 |issue=10 |pages=2093–2100}}</ref> [[Coordination number|3-Coordinate]] chlorocuprate(II) complexes are rare.<ref>{{cite journal |doi=10.1002/1521-3765(20020315)8:6<1269::AID-CHEM1269>3.0.CO;2-9 |title=Three-Coordinate [Cu<sup>II</sup>X<sub>3</sub>]<sup>−</sup> (X = Cl, Br), Trapped in a Molecular Crystal |year=2002 |last1=Hasselgren |first1=Catrin |last2=Jagner |first2=Susan |last3=Dance |first3=Ian |journal=Chemistry – A European Journal |volume=8 |issue=6 |pages=1269–1278| pmid=11921210}}</ref>

Tetrachlorocuprate(II) complexes tend to adopt flattened [[tetrahedral geometry]] with orange colors.<ref>{{cite journal |doi=10.1107/S0108270196009031|title=Tetraethylammonium Tetramethylammonium Tetrachlorocuprate(II), [(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>N][(CH<sub>3</sub>)<sub>4</sub>N][CuCl<sub>4</sub>] |year=1996 |last1=Mahoui |first1=A. |last2=Lapasset |first2=J. |last3=Moret |first3=J. |last4=Saint Grégoire |first4=P. |journal=Acta Crystallographica Section C |volume=52 |issue=11 |pages=2674–2676}}</ref><ref>{{cite journal |title=Reversible Extrusion and Uptake of HCl Molecules by Crystalline Solids Involving Coordination Bond Cleavage and Formation |author1=Guillermo Mínguez Espallargas |author2=Lee Brammer |author3=Jacco van de Streek |author4=Kenneth Shankland |author5=Alastair J. Florence |author6=Harry Adams |journal=[[Journal of the American Chemical Society|J. Am. Chem. Soc.]]| year=2006 |volume=128 |issue=30 |pages=9584–9585 |doi=10.1021/ja0625733 |pmid=16866484}}</ref><ref>{{cite journal |title=The square-planar to flattened-tetrahedral CuX<sub>4</sub><sup>2−</sup> (''X'' = Cl, Br) structural phase transition in 1,2,6-trimethylpyridinium salts |first1=A. |last1=Kelley |first2=S. |last2=Nalla |first3=M. R. |last3=Bond |journal=[[Acta Crystallographica|Acta Crystallogr. B]] |year=2015 |volume=71 |issue=Pt 1 |pages=48–60 |doi=10.1107/S205252061402664X |pmid=25643715}}</ref><ref>{{cite book |url=https://books.google.com/books?id=vEwj1WZKThEC&pg=PA1264 |pages=1252–1264 |title=Inorganic Chemistry |author1=Egon Wiberg |author2=Nils Wiberg |author3=Arnold Frederick Holleman |publisher=Academic Press |year=2001 |isbn=0-12-352651-5}}</ref>

Sodium tetrahydroxycuprate(II) ({{chem2|Na2[Cu(OH)4]}}) is an example of a [[homoleptic]] (all [[ligands]] being the same) [[hydroxide]] complex.<ref>{{cite book|entry=Sodium Tetrahydroxocuprate(II) |title=Handbook of Preparative Inorganic Chemistry |edition=2nd |editor-first=G. |editor-last=Brauer |publisher=Academic Press |date=1963 |location=New York, NY |volume=1 |page=1015}}</ref>
:{{chem2|Cu(OH)2 + 2 NaOH → Na2[Cu(OH)4]}}

===Copper(III) and copper(IV)===
[[Potassium hexafluorocuprate(III)|Hexafluorocuprate(III)]] {{chem2|[CuF6](3−)}} and [[Caesium hexafluorocuprate(IV)|hexafluorocuprate(IV)]] {{chem2|[CuF6](2−)}} are rare examples of copper(III) and copper(IV) complexes. They are strong [[oxidizing agent]]s.

==Organic cuprates==
[[File:Lithium-diphenylcuprate-etherate-dimer-from-xtal-2D-skeletal.png|thumb|upright|Structure of lithium diphenylcuprate(I) etherate, {{chem2|2[[Phenyl|Ph]]2Cu]−Li+*2[[Diethyl ether|OEt2]]}}.<ref>{{cite journal|doi=10.1002/anie.199003001|title=Synthesis and Structure of a Dimeric Lithium Diphenylcuprate:[{Li(OEt<sub>2</sub>)}(CuPh<sub>2</sub>)]<sub>2</sub> |year=1990 |last1=Lorenzen |first1=Nis Peter |last2=Weiss |first2=Erwin |journal=Angewandte Chemie International Edition in English |volume=29 |issue=3 |pages=300}}</ref>]]

{{main|Organocopper compound}}
Cuprates have a role in [[organic synthesis]]. They are invariably Cu(I), although Cu(II) or even Cu(III) [[Reactive intermediate|intermediate]]s are invoked in some [[chemical reactions]]. Organic cuprates often have the idealized formulas {{chem2|[CuR2]−}} and {{chem2|[CuR3](2−)}}, 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 reagent]]s.<ref>{{cite book |url=https://books.google.com/books?id=101pNv3QpEIC&pg=PA61 |pages=61–65 |title=Transition metals in the synthesis of complex organic molecules |author=Louis S. Hegedus |publisher=University Science Books |year=1999 |isbn=1-891389-04-1}}</ref>

==See also==
*[[Cuprate superconductor]]
*[[High-temperature superconductivity]]
*[[Gilman reagent]]
==References==
{{reflist|30em}}

{{Copper compounds}}

[[Category:Copper compounds]]
[[Category:Anions]]
[[Category:Transition metal oxyanions]]
[[Category:Oxometallates]]