Cuprate
{{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. They can be broadly categorized into two main types:
1. Inorganic cuprates: These compounds have a general formula of {{chem2|XYCu_{m}O_{n}|}}. Some of them are non-stoichiometric. Many of these compounds are known for their superconducting properties.{{cn|date=January 2024}} An example of an inorganic cuprate is the tetrachloridocuprate(II) or tetrachlorocuprate(II) ({{chem2|[CuCl4](2-)|auto=1}}), an anionic coordination complex that features a copper atom in an oxidation state of +2, surrounded by four chloride ions.
2. Organic cuprates: These are organocopper compounds, some of which having a general formula of {{chem2|[CuR2]−}}, where copper is in an oxidation state of +1, where at least one of the R groups can be any organic group. These compounds, characterized by copper bonded to organic groups, are frequently used in organic synthesis due to their reactivity.{{cn|date=January 2024}} An example of an organic cuprate is dimethylcuprate(I) anion {{chem2|[Cu(CH3)2]-}}.
One of the most studied cuprates is {{chem2|YBa2Cu3O7|auto=1}}, a high-temperature superconducting material. This oxide cuprate has been the subject of extensive research due to its ability to conduct electricity without resistance at relatively high temperatures.{{cn|date=January 2024}}
The term 'cuprate' originates from 'cuprum', the Latin word for copper. It is primarily used in the context of oxide materials, anionic coordination complexes, and anionic organocopper compounds, reflecting the diverse roles of copper in chemistry. The term is mainly used in three contexts: oxide materials, anionic coordination complexes, and anionic organocopper compounds.{{cn|date=January 2024}}
Oxide cuprates
Many stable or metastable alkali metal cuprates(III) are known, all salts of the polyanion {{chem2|[CuO2−]_{n}|}}. They are strong oxidants, oxidizing water. They are typically produced through extremely large oxygen activities. Alkali metals larger than sodium produce dark-blue salts,{{cite journal |last1=Costa |first1=Giorgio A. |last2=Kaiser |first2=Elena |title=Structural and thermal properties of the alkaline cuprate KCuO2 |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 }} but sodium cuprate(III) is red-brown.{{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=}}
One of the simplest oxide-based cuprates is potassium cuprate(III) {{chem2|KCuO2}}.{{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}} 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 defects in the crystal structure, and this leads to the tendency of this compound to be reduced.
Coordination complexes
Copper forms many anionic coordination complexes with negatively charged ligands such as cyanide, hydroxide, and halides, as well as alkyls and aryls.
=Copper(I)=
Cuprates containing copper(I) tend to be colorless, reflecting their d10 configuration. Structures range from linear 2-coordinate, trigonal planar, and tetrahedral molecular geometry. Examples include linear {{chem2|[CuCl2]−}} and trigonal planar {{chem2|[CuCl3](2−)}}.{{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}} Cyanide gives analogous complexes but also the trianionic tetracyanocuprate(I), {{chem2|[Cu(CN)4](3−)}}.{{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}} Dicyanocuprate(I), {{chem2|[Cu(CN)2]−}}, exists in both molecular or polymeric motifs, depending on the countercation.{{cite journal |doi=10.1021/ic000399s |title=Crystal Structures and Vibrational Spectroscopy of [NBu4][Cu(CN)X] (X = Br, I) and [NBu4][Cu3(CN)4]·CH3CN |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}}
=Copper(II)=
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−)}}.{{Greenwood&Earnshaw2nd}}{{cite journal |doi=10.1016/j.poly.2006.01.005|title=Two Halide Exchange in Copper(II) Halide Dimers: (4,4{{prime}}-Bipyridinium)Cu2Cl6−x 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}} 3-Coordinate chlorocuprate(II) complexes are rare.{{cite journal |doi=10.1002/1521-3765(20020315)8:6<1269::AID-CHEM1269>3.0.CO;2-9 |title=Three-Coordinate [CuIIX3]− (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}}
Tetrachlorocuprate(II) complexes tend to adopt flattened tetrahedral geometry with orange colors.{{cite journal |doi=10.1107/S0108270196009031|title=Tetraethylammonium Tetramethylammonium Tetrachlorocuprate(II), [(C2H5)4N][(CH3)4N][CuCl4] |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}}{{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=J. Am. Chem. Soc.| year=2006 |volume=128 |issue=30 |pages=9584–9585 |doi=10.1021/ja0625733 |pmid=16866484}}{{cite journal |title=The square-planar to flattened-tetrahedral CuX42− (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 Crystallogr. B |year=2015 |volume=71 |issue=Pt 1 |pages=48–60 |doi=10.1107/S205252061402664X |pmid=25643715}}{{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}}
Sodium tetrahydroxycuprate(II) ({{chem2|Na2[Cu(OH)4]}}) is an example of a homoleptic (all ligands being the same) hydroxide complex.{{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}}
:{{chem2|Cu(OH)2 + 2 NaOH → Na2[Cu(OH)4]}}
=Copper(III) and copper(IV)=
Hexafluorocuprate(III) {{chem2|[CuF6](3−)}} and hexafluorocuprate(IV) {{chem2|[CuF6](2−)}} are rare examples of copper(III) and copper(IV) complexes. They are strong oxidizing agents.
Organic cuprates
File:Lithium-diphenylcuprate-etherate-dimer-from-xtal-2D-skeletal.png2Cu]−Li+*2OEt2}}.{{cite journal|doi=10.1002/anie.199003001|title=Synthesis and Structure of a Dimeric Lithium Diphenylcuprate:[{Li(OEt2)}(CuPh2)]2 |year=1990 |last1=Lorenzen |first1=Nis Peter |last2=Weiss |first2=Erwin |journal=Angewandte Chemie International Edition in English |volume=29 |issue=3 |pages=300}}]]
{{main|Organocopper compound}}
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 {{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 reagents.{{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}}