Copper compounds
{{Short description|Chemical compounds containing copper}}
Copper forms a rich variety of compounds, usually with oxidation states +1 and +2, which are often called cuprous and cupric, respectively. Copper compounds, whether organic complexes or organometallics, promote or catalyse numerous chemical and biological processes.{{cite journal |last1=Trammell |first1=Rachel |last2=Rajabimoghadam |first2=Khashayar |last3=Garcia-Bosch |first3=Isaac |title=Copper-Promoted Functionalization of Organic Molecules: from Biologically Relevant Cu/O2 Model Systems to Organometallic Transformations|journal=Chemical Reviews |volume=119 |issue=4 |pages=2954–3031 |date=30 January 2019 |doi=10.1021/acs.chemrev.8b00368|pmid=30698952 |pmc=6571019 }}
Binary compounds
As with other elements, the simplest compounds of copper are binary compounds, i.e. those containing only two elements, the principal examples being oxides, sulfides, and halides. Both cuprous and cupric oxides are known. Among the numerous copper sulfides, important examples include copper(I) sulfide and copper(II) sulfide.{{Citation needed|date=January 2021}}
Cuprous halides with fluorine, chlorine, bromine, and iodine are known, as are cupric halides with fluorine, chlorine, and bromine. Attempts to prepare copper(II) iodide yield only copper(I) iodide and iodine.{{cite book |last1=Holleman |first1=A.F. |last2=Wiberg |first2=N. |title=Inorganic Chemistry |date=2001 |publisher=Academic Press |location=San Diego |isbn=978-0-12-352651-9}}
:2 Cu2+ + 4 I− → 2 CuI + I2
Coordination chemistry
=Cu–O and Cu–N complexes=
Copper forms coordination complexes with ligands. 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 for copper in uncomplexed media (anions other than OH− not considered). Ion concentration 0.001 m (mol/kg water). Temperature 25 °C.]]
:Cu2+ + 2 OH− → Cu(OH)2
Aqueous ammonia results in the same precipitate. Upon adding excess ammonia, the precipitate dissolves, forming tetraamminecopper(II):
:{{chem|Cu|(H|2|O)|4|(OH)|2}} + 4 NH3 → {{chem|[Cu|(H|2|O)|2|(N|H|3|)|4|]|2+}} + 2 H2O + 2 OH−
Many other oxyanions form complexes; these include copper(II) acetate, copper(II) nitrate, and copper(II) carbonate. Copper(II) sulfate forms a blue crystalline pentahydrate, the most familiar copper compound in the laboratory. It is used in a fungicide called the Bordeaux mixture.{{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 }}
File:Tetraamminediaquacopper(II)-3D-balls.png of the complex [Cu(NH3)4(H2O)2]2+, illustrating the octahedral coordination geometry common for copper(II).]]
Polyols, 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.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}} Schweizer's reagent and related complexes with ethylenediamine and other amines dissolve cellulose.{{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 }} Amino acids such as cystine form very stable chelate complexes with copper(II).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.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.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 Many wet-chemical tests for copper ions exist, one involving potassium ferrocyanide, which gives a brown precipitate with copper(II) salts.{{Citation needed|date=January 2021}}
=Cu–X complexes=
Copper also forms complexes with halides. In Cs2CuCl4, CuCl42− exhibits a distorted (flattened) tetrahedral geometry, whereas in [Pt(NH3)4][CuCl4], it adopts a planar configuration. Green CuBr3− and violet CuBr42− are also known.{{cite journal| author=R.A. Howald; D.P. Keeton|year=1966|title=Charge transfer spectra and structure of the copper (II) halide complexes|volume=22|issue=7|pages=1211–1222|journal=Spectrochimica Acta|doi=10.1016/0371-1951(66)80024-3|bibcode=1966AcSpe..22.1211H }} Monovalent copper forms luminescent CunXn clusters (where X = Br, Cl, I), exhibiting diverse optical properties.{{cite journal|author=Abraham Mensah; Juan-Juan Shao; Jian-Ling Ni; Guang-Jun Li; Fang-Ming Wang; Li-Zhuang Chen|title=Recent Progress in Luminescent Cu(I) Halide Complexes: A Mini-Review|year=2022|volume=9|doi=10.3389/fchem.2021.816363|journal=Frontiers in Chemistry|page=1127 |doi-access=free |pmid=35145957 |pmc=8822502|bibcode=2022FrCh....9.1127W }}{{cite journal|author=Hiromi Araki, Kiyoshi Tsuge, Yoichi Sasaki, Shoji Ishizaka, and Noboru Kitamura|title=Luminescence Ranging from Red to Blue: A Series of Copper(I)−Halide Complexes Having Rhombic {Cu2(μ-X)2} (X = Br and I) Units with N-Heteroaromatic Ligands|journal=Inorg. Chem.|year=2005|volume=44|issue=26| pages=9667–9675 |doi=10.1021/ic0510359| pmid=16363835 }}
Organocopper chemistry
{{Main|Organocopper chemistry}}
Compounds that contain a carbon-copper bond are known as organocopper compounds. They are very reactive towards oxygen to form copper(I) oxide and have many uses in chemistry. They are synthesized by treating copper(I) compounds with Grignard reagents, terminal alkynes or organolithium reagents;"Modern Organocopper Chemistry" Norbert Krause, Ed., Wiley-VCH, Weinheim, 2002. {{ISBN|978-3-527-29773-3}}. in particular, the last reaction described produces a Gilman reagent. These can undergo substitution with alkyl halides to form coupling products; as such, they are important in the field of organic synthesis. Copper(I) acetylide is highly shock-sensitive but is an intermediate in reactions such as the Cadiot-Chodkiewicz coupling{{cite journal|last1=Berná|first1=José|last2=Goldup|first2=Stephen|last3=Lee|first3=Ai-Lan|last4=Leigh|first4=David|last5=Symes|first5=Mark|last6=Teobaldi|first6=Gilberto|last7=Zerbetto|first7=Fransesco|title=Cadiot–Chodkiewicz Active Template Synthesis of Rotaxanes and Switchable Molecular Shuttles with Weak Intercomponent Interactions|journal=Angewandte Chemie|date=26 May 2008|volume=120|issue=23|pages=4464–4468|doi=10.1002/ange.200800891|bibcode=2008AngCh.120.4464B}} and the Sonogashira coupling.{{cite journal|title = The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry|author = Rafael Chinchilla|author2 = Carmen Nájera|name-list-style = amp|journal = Chemical Reviews|date = 2007|volume = 107|issue = 3|pages = 874–922|doi = 10.1021/cr050992x|pmid = 17305399}} Conjugate addition to enones{{cite journal|date=1986 |title=An Addition of an Ethylcopper Complex to 1-Octyne: (E)-5-Ethyl-1,4-Undecadiene |journal=Organic Syntheses |volume=64 |page=1 |doi=10.15227/orgsyn.064.0001 }} and carbocupration of alkynes{{cite journal |last1=Kharasch |first1=M.S. |last2=Tawney |first2=P.O. |date=1941|title=Factors Determining the Course and Mechanisms of Grignard Reactions. II. The Effect of Metallic Compounds on the Reaction between Isophorone and Methylmagnesium Bromide |journal=Journal of the American Chemical Society |volume=63 |issue=9 |pages=2308–2316 |doi=10.1021/ja01854a005|bibcode=1941JAChS..63.2308K }} can also be achieved with organocopper compounds. Copper(I) forms a variety of weak complexes with alkenes and carbon monoxide, especially in the presence of amine ligands.{{cite journal|last1= Imai |first1= Sadako |last2= Fujisawa |first2= Kiyoshi |last3= Kobayashi |first3= Takako |last4= Shirasawa |first4= Nobuhiko |last5= Fujii |first5= Hiroshi |last6= Yoshimura |first6= Tetsuhiko |last7= Kitajima |first7= Nobumasa |last8= Moro-oka |first8= Yoshihiko |title= 63Cu NMR Study of Copper(I) Carbonyl Complexes with Various Hydrotris(pyrazolyl)borates: Correlation between 63Cu Chemical Shifts and CO Stretching Vibrations|journal= Inorganic Chemistry |date= 1998| volume =37|pages=3066–3070|doi=10.1021/ic970138r|issue=12}}
Copper(III) and copper(IV)
Copper(III) is most often found in oxides. A simple example is potassium cuprate, KCuO2, a blue-black solid.{{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=1|page=1015}} The most extensively studied copper(III) compounds are the cuprate superconductors. Yttrium barium copper oxide (YBa2Cu3O7) consists of both Cu(II) and Cu(III) centres. Like oxide, fluoride is a highly basic anion{{cite journal|author1=Schwesinger, Reinhard |author2=Link, Reinhard |author3=Wenzl, Peter |author4=Kossek, Sebastian |title=Anhydrous phosphazenium fluorides as sources for extremely reactive fluoride ions in solution|doi=10.1002/chem.200500838|year=2006|journal=Chemistry: A European Journal|volume=12|issue=2|pages=438–45 |pmid=16196062}} and is known to stabilize metal ions in high oxidation states. Both copper(III) and even copper(IV) fluorides are known, K3CuF6 and Cs2CuF6, respectively.
Some copper proteins form oxo complexes, which also feature copper(III).{{cite journal |last1=Lewis |first1=E.A. |last2=Tolman |first2=W.B. |date=2004 |title=Reactivity of Dioxygen-Copper Systems |journal=Chemical Reviews |volume=104 |pages=1047–1076 |doi=10.1021/cr020633r |issue=2 |pmid=14871149}} With tetrapeptides, purple-colored copper(III) complexes are stabilized by the deprotonated amide ligands.{{cite journal |last1=McDonald |first1=M.R. |last2=Fredericks |first2=F.C. |last3=Margerum |first3=D.W. |date=1997 |title=Characterization of Copper(III)–Tetrapeptide Complexes with Histidine as the Third Residue |journal=Inorganic Chemistry |volume=36 |pages=3119–3124|doi=10.1021/ic9608713|pmid=11669966 |issue=14}}
Complexes of copper(III) are also found as intermediates in reactions of organocopper compounds.{{Greenwood&Earnshaw2nd|page=1187}} For example, in the Kharasch–Sosnovsky reaction.{{Citation needed|date=January 2021}}