anionic coordination complexes with negatively charged ligands such as cyanide, hydroxide, 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. Examples include dichloro and trichlorocuprates, i.e., linear [CuCl2]− and trigonal planar [CuCl3]2−. Cyanide gives analogous complexes but also the trianionic tetracyanocuprate(I), [Cu(CN)4]3−. Dicyanocuprate(I) exists in both molecular or polymeric motifs, depending on the countercation. Copper(II) The chlorocuprates include trichlorocuprate(II) [CuCl3]−, which is dimeric, square-planar tetrachlorocuprate(II) [CuCl4]2−, and pentachlorocuprate(II) [CuCl5]3−. 3-Coordinate chlorocuprate(II) complexes are rare. Tetrachlorocuprate(II) complexes tend to adopt flattened tetrahedral geometry with orange colors. Sodium tetrahydroxycuprate (Na2[Cu(OH)4]) is an example of a homoleptic (all ligands being the same) hydroxide complex. Cu(OH)2 + 2 NaOH → Na2Cu(OH)4 Copper(III) and copper(IV) Hexafluorocuprate(III) [CuF6]3− and hexafluorocuprate(IV) [CuF6]2− are rare examples of copper(III) and copper(IV) complexes. They are strong oxidizing agents. Organic cuprates Cuprates have a role in organic synthesis. They are invariably Cu(I), although Cu(II) or even Cu(III) intermediates are invoked in some mechanisms. Organic cuprates often have the idealized formulas [CuR2]− and [CuR3]2−, where R is an alkyl or aryl. These reagents find use as nucleophilic alkylating reagents. See also Cuprate superconductor High-temperature superconductivity Gilman reagent References Copper compounds Anions Oxometallates Transition metal oxyanions