Editing Copper (section)

===Coordination chemistry===
[[File:Tetramminkupfer(II)-sulfat-Monohydrat Kristalle.png|thumb|left|Copper(II) gives a deep blue coloration in the presence of ammonia ligands. The one used here is [[tetraamminecopper(II) sulfate]].]]
Copper forms [[coordination complex]]es with [[ligand]]s. In aqueous solution, copper(II) exists as {{chem|[Cu|(H|2|O)|6|]|2+}}. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition [[metal aquo complex]]. Adding aqueous [[sodium hydroxide]] causes the precipitation of light blue solid [[copper(II) hydroxide]]. A simplified equation is: [[File:Cu-pourbaix-diagram.svg|thumbnail|Pourbaix diagram for copper in uncomplexed media (anions other than OH- not considered). Ion concentration 0.001&nbsp;m (mol/kg water). Temperature 25&nbsp;°C.]]
:Cu<sup>2+</sup> + 2 OH<sup>−</sup> → Cu(OH)<sub>2</sub>
[[Ammonia solution|Aqueous ammonia]] results in the same precipitate. Upon adding excess ammonia, the precipitate dissolves, forming [[Schweizer's reagent|tetraamminecopper(II)]]:
:{{chem|Cu|(H|2|O)|4|(OH)|2}} + 4 NH<sub>3</sub> → {{chem|[Cu|(H|2|O)|2|(N|H|3|)|4|]|2+}} + 2 H<sub>2</sub>O + 2 OH<sup>−</sup>
Many other [[oxyanion]]s form complexes; these include [[copper(II) acetate]], [[copper(II) nitrate]], and [[copper(II) carbonate]]. [[Copper(II) sulfate]] forms a blue crystalline penta[[hydrate]], the most familiar copper compound in the laboratory. It is used in a [[fungicide]] called the [[Bordeaux mixture]].<ref name="Boux">{{cite book|chapter-url = https://books.google.com/books?id=cItuoO9zSjkC&pg=PA623|page = 623|chapter = Nonsystematic (Contact) Fungicides|title = Ullmann's Agrochemicals|isbn = 978-3-527-31604-5|author1 = Wiley-Vch|date = 2 April 2007| publisher=Wiley }}</ref>
[[File:Tetraamminediaquacopper(II)-3D-balls.png|thumb|right|upright=0.9|[[Ball-and-stick model]] of the complex [Cu(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup>, illustrating the [[octahedral coordination geometry]] common for copper(II)]]

[[Polyol]]s, compounds containing more than one alcohol [[functional group]], generally interact with cupric salts. For example, copper salts are used to test for [[reducing sugars]]. Specifically, using [[Benedict's reagent]] and [[Fehling's solution]] the presence of the sugar is signaled by a color change from blue Cu(II) to reddish copper(I) oxide.<ref>Ralph L. Shriner, Christine K.F. Hermann, Terence C. Morrill, David Y. Curtin, Reynold C. Fuson "The Systematic Identification of Organic Compounds" 8th edition, J. Wiley, Hoboken. {{ISBN|0-471-21503-1}}</ref> Schweizer's reagent and related complexes with [[ethylenediamine]] and other [[amine]]s dissolve [[cellulose]].<ref>{{cite journal | last1 = Saalwächter | first1 = Kay | last2 = Burchard | first2 = Walther | last3 = Klüfers | first3 = Peter | last4 = Kettenbach | first4 = G. | last5 = Mayer | first5 = Peter | last6 = Klemm | first6 = Dieter | last7 = Dugarmaa | first7 = Saran | year = 2000 | title = Cellulose Solutions in Water Containing Metal Complexes | journal = Macromolecules | volume = 33 | issue = 11| pages = 4094–4107 | doi = 10.1021/ma991893m | bibcode = 2000MaMol..33.4094S | citeseerx = 10.1.1.951.5219 }}</ref> [[Amino acid]]s such as cystine form very stable [[chelate complex]]es with copper(II)<ref>Deodhar, S., Huckaby, J., Delahoussaye, M. and DeCoster, M.A., 2014, August. High-aspect ratio bio-metallic nanocomposites for cellular interactions. In IOP Conference Series: Materials Science and Engineering (Vol. 64, No. 1, p. 012014). https://iopscience.iop.org/article/10.1088/1757-899X/64/1/012014/meta.</ref><ref>Kelly, K.C., Wasserman, J.R., Deodhar, S., Huckaby, J. and DeCoster, M.A., 2015. Generation of scalable, metallic high-aspect ratio nanocomposites in a biological liquid medium. Journal of Visualized Experiments, (101), p.e52901. https://www.jove.com/t/52901/generation-scalable-metallic-high-aspect-ratio-nanocomposites.</ref><ref>Karan, A., Darder, M., Kansakar, U., Norcross, Z. and DeCoster, M.A., 2018. Integration of a Copper-Containing Biohybrid (CuHARS) with Cellulose for Subsequent Degradation and Biomedical Control. International journal of environmental research and public health, 15(5), p.844. https://www.mdpi.com/1660-4601/15/5/844</ref> including in the form of [[metal-organic biohybrid]]s (MOBs).  Many wet-chemical tests for copper ions exist, one involving [[potassium ferricyanide]], which gives a red-brown precipitate with copper(II) salts.<ref>{{Cite web |date=2018-04-03 |title=Characteristic Reactions of Copper Ions (Cu²⁺) |url=https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Qualitative_Analysis/Characteristic_Reactions_of_Select_Metal_Ions/Characteristic_Reactions_of_Copper_Ions_(Cu) |access-date=2024-05-27 |website=Chemistry LibreTexts |language=en}}</ref>