Editing Copper(II) chloride (section)

==Properties and reactions==
[[File:CuCl2 equilibrium.JPG|thumb|left|Aqueous solutions of copper(II) chloride. Greenish when high in {{chem2|Cl−}}, more blue when lower in {{chem2|Cl−}}.]]
Aqueous solutions prepared from copper(II) chloride contain a range of copper(II) [[coordination complex|complexes]] depending on [[concentration]], temperature, and the presence of additional [[chloride|chloride ions]]. These species include the blue color of {{chem2|[Cu(H2O)6](2+)}} and the yellow or red color of the halide complexes of the formula {{chem2|[CuCl_{2+''x''}]^{''x''−}|}}.<ref name="greenwood">Greenwood, N. N. and Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. p. 1183–1185 {{ISBN|0-7506-3365-4}}.</ref>

===Hydrolysis===
When copper(II) chloride solutions are treated with a [[base (chemistry)|base]], a [[precipitation (chemistry)|precipitation]] of [[copper(II) hydroxide]] occurs:<ref name="Ullmann" />
:{{chem2|CuCl2 + 2 NaOH → Cu(OH)2 + 2 NaCl}}

Partial hydrolysis gives [[dicopper chloride trihydroxide]], {{chem2|Cu2(OH)3Cl}}, a popular fungicide.<ref name="Ullmann" /> When an aqueous solution of copper(II) chloride is left in the air and isn't stabilized by a small amount of acid, it is prone to undergo slight hydrolysis.<ref name="greenwood" />

===Redox and decomposition===
Copper(II) chloride is a mild [[oxidizing agent|oxidant]]. It starts to decompose to [[copper(I) chloride]] and [[Chlorine|chlorine gas]] around {{convert|400|C}} and is completely decomposed near {{convert|1000|C}}:<ref name="Ullmann">{{Cite book|title=Ullmann's Encyclopedia of Industrial Chemistry|author1=Zhang, J. |author2=Richardson, H. W.|year=2016|isbn=978-3-527-30673-2|chapter=Copper Compounds|pages=1–31 |doi=10.1002/14356007.a07_567.pub2}}</ref><ref name="tgdta">{{cite journal |author1=Shuiliang Zhou |author2=Shaobo Shen |author3=Dalong Zhao |author4=Zhitao Zhang |author5=Shiyu Yan |title=Evaporation and decomposition of eutectics of cupric chloride and sodium chloride |journal=Journal of Thermal Analysis and Calorimetry |date=2017 |volume=129 |issue=3 |pages=1445–1452 |doi=10.1007/s10973-017-6360-y |s2cid=99924382 |language=en}}</ref><ref name="Kirk">{{Cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last=Richardson|first=H. W.|year=2003|isbn=0471238961|chapter=Copper Compounds|doi=10.1002/0471238961.0315161618090308.a01.pub2}}</ref><ref name="cucl">{{cite journal |author1=Z. Wang |author2=G. Marin |author3=G. F. Naterer |author4=K. S. Gabriel |title=Thermodynamics and kinetics of the thermal decomposition of cupric chloride in its hydrolysis reaction |journal=Journal of Thermal Analysis and Calorimetry |date=2015 |volume=119 |issue=2 |pages=815–823 |doi=10.1007/s10973-014-3929-6 |s2cid=93668361 |url=https://research.library.mun.ca/13446/1/2015-JTAC.pdf |language=en}}</ref>
:{{chem2|2 CuCl2 → 2 CuCl + Cl2}}
The reported [[melting point]] of copper(II) chloride of {{convert|498|C}} is a melt of a mixture of copper(I) chloride and copper(II) chloride. The true melting point of {{convert|630|C}} can be extrapolated by using the melting points of the mixtures of CuCl and {{chem2|CuCl2}}.<ref>{{cite journal |author1=Wilhelm Biltz |author2=Werner Fischer |title=Beiträge zur systematischen Verwandtschaftslehre. XLIII. Über das System Cupro-/Cuprichlorid |journal=Zeitschrift für anorganische und allgemeine Chemie |date=1927 |volume=166 |issue=1 |pages=290–298 |doi=10.1002/zaac.19271660126 |language=de}}</ref><ref name="group">{{cite book |author1=A. G. Massey |author2=N. R. Thompson |author3=B. F. G. Johnson |title=The Chemistry of Copper, Silver and Gold |date=1973 |publisher=Elsevier Science |isbn=9780080188607 |language=en |page=42}}</ref> Copper(II) chloride reacts with several metals to produce copper metal or copper(I) chloride (CuCl) with oxidation of the other metal. To convert copper(II) chloride to copper(I) chloride, it can be convenient to reduce an aqueous solution with [[sulfur dioxide]] as the [[reducing agent|reductant]]:<ref name="Ullmann" />
:{{chem2|2 CuCl2 + SO2 + 2 H2O → 2 CuCl + 2 HCl + H2SO4}}

===Coordination complexes===
{{chem2|CuCl2}} reacts with HCl or other [[chloride]] sources to form complex ions: the red {{chem2|[CuCl3]−}} (found in [[potassium trichloridocuprate(II)]] {{chem2|K[CuCl3]}}) (it is a [[dimerization (chemistry)|dimer]] in reality, {{chem2|[Cu2Cl6](2−)}}, a couple of tetrahedrons that share an edge), and the green or yellow {{chem2|[CuCl4](2−)}} (found in [[potassium tetrachloridocuprate(II)]] {{chem2|K2[CuCl4]}}).<ref name="greenwood" /><ref name="tetra">{{cite book|author=Naida S. Gill |author2=F. B. Taylor |series=Inorganic Syntheses |year=1967 |volume=9 |pages=136–142 |doi=10.1002/9780470132401.ch37 |title=Tetrahalo Complexes of Dipositive Metals in the First Transition Series |isbn=978-0-470-13240-1}}</ref><ref name="handbook" />

:{{chem2|CuCl2 + Cl- ⇌ [CuCl3]-}} 
:{{chem2|CuCl2 + 2 Cl- ⇌ [CuCl4](2-)}}

Some of these complexes can be crystallized from aqueous solution, and they adopt a wide variety of structures.<ref name="tetra" />

Copper(II) chloride also forms a variety of [[complex (chemistry)|coordination complexes]] with [[ligand]]s such as [[ammonia]], [[pyridine]] and [[triphenylphosphine oxide]]:<ref name="Ullmann" /><ref name="greenwood" /><ref>{{cite journal |author1=W. Libus |author2=S. K. Hoffmann |author3=M. Kluczkowski |author4=H. Twardowska |title=Solution equilibriums of copper(II) chloride in pyridine and pyridine-diluent mixtures |journal=Inorganic Chemistry |date=1980 |volume=19 |issue=6 |pages=1625–1632 |doi=10.1021/ic50208a039 |language=en}}</ref>
:{{chem2|CuCl2 + 2 C5H5N → [CuCl2(C5H5N)2]}} (tetragonal)
:{{chem2|CuCl2 + 2 (C6H5)3P\dO → [CuCl2((C6H5)3P\dO)2]}} (tetrahedral)
However "soft" ligands such as [[phosphine]]s (e.g., [[triphenylphosphine]]), iodide, and [[cyanide]] as well as some tertiary [[amine]]s induce [[Redox|reduction]] to give copper(I) complexes.<ref name="greenwood" />