Cuprate

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Cuprate loosely refers to a material that can be viewed as containing anionic copper complexes. Examples include tetrachloridocuprate ([CuCl4]2−), the superconductor YBa2Cu3O7, and the organocuprates (e.g., dimethylcuprate [Cu(CH3)2]).[1] The term cuprates derives from the Latin word for copper, cuprum. The term is mainly used in three contexts - oxide materials, anionic coordination complexes, and anionic organocopper compounds.

Oxides[edit]

One of the simplest oxide-based cuprates is the copper(III) oxide KCuO2. This species can be viewed as the K+ salt of the polyanion [CuO
2
]n. As such the material is classified as a cuprate. This dark blue diamagnetic solid is produced by heating potassium peroxide and copper(II) oxide in an atmosphere of oxygen:[2]

K2O2 + 2 CuO → 2 KCuO2

Coordination complexes[edit]

Copper forms many anionic "cuprate" coordination complexes with negatively charged ligands such as cyanide, hydroxide, and halides. Copper(I) derivatives tend to be colorless, copper(II) complexes are often turquoise-blue, and copper(III) and copper(IV) complexes are often orange-red.[3]

Hexafluorocuprate(IV)

One example of a copper(I)-based cuprate is the tetrahedral complex tetracyanocuprate(I), [Cu(CN)4]3−.[4]

Copper(II) anions are most common, especially the chlorocuprates, such as trichlorocuprate(II) [CuCl3], tetrachlorocuprate(II) [CuCl4]2− and pentachlorocuprate(II) [CuCl5]3−.[1] The light blue solid sodium tetrahydroxycuprate is well known; it is prepared by heating cupric hydroxide with concentrated sodium hydroxide.[5]

Cu(OH)2 + 2 NaOH → Na2Cu(OH)4

Dilithium tetrachlorocuprate (Li2CuCl4) is an effective catalyst for the couplings of Grignard reagents. It is prepared by mixing lithium chloride (LiCl) and copper(II) chloride (CuCl2) in tetrahydrofuran.[6]

There are also rare copper(III) and copper(IV) complexes such as the hexafluorocuprate(III) [CuF6]3− and hexafluorocuprate(IV) [CuF6]2−, which are strong oxidizing agents.

Organic cuprates[edit]

Cuprates have a role in organic synthesis. Organic cuprates often have the formula [CuR2] or [CuR3]2−, where R is an alkyl or aryl. These reagents find use as nucleophilic alkylating reagents. In stark contrast to the oxidic cuprates, the handling of these organocopper requires air-free techniques.[7]

Organocopper aggregates containing more than one copper atom
Skeletal formula of a dimer from the crystal structure of lithium diphenylcuprate etherate, 2Ph2CuLi·2OEt2[8]

See also[edit]

References[edit]

  1. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  2. ^ G. Brauer, ed. (1963). "Potassium Cuprate (III)". Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). NY: Academic Press. p. 1015.
  3. ^ Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 1252–1264. ISBN 0-12-352651-5.
  4. ^ [1]
  5. ^ "Sodium Tetrahydroxocuprate (II) in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1015.
  6. ^ Atta-ur-Rahman (2002). Bioactive natural products. Elsevier. pp. 73, 81, 83. ISBN 0-444-51004-4.
  7. ^ Louis S. Hegedus (1999). Transition metals in the synthesis of complex organic molecules. University Science Books. pp. 61–65. ISBN 1-891389-04-1.
  8. ^ Lorenzen, Nis Peter; Weiss, Erwin (1990). "Synthesis and Structure of a Dimeric Lithium Diphenylcuprate:[{Li(OEt)2}(CuPh2)]2". Angewandte Chemie International Edition in English. 29 (3): 300. doi:10.1002/anie.199003001.