copper(II) nitrate

Hydrated copper nitrate is prepared by treating copper metal or its oxide with nitric acid:

:{{chem2|Cu + 4 HNO3 -> Cu(NO3)2 + 2 H2O + 2 NO2}}

The same salts can be prepared treating copper metal with an aqueous solution of silver nitrate. That reaction illustrates the ability of copper metal to reduce silver ions.

In aqueous solution, the hydrates exist as the aqua complex {{chem2|[Cu(H2O)6](2+)}}. Such complexes are highly labile and subject to rapid ligand exchange due to the d⁹ electronic configuration of copper(II).

Attempted dehydration of any of the hydrated copper(II) nitrates by heating affords the oxides, not {{chem2|Cu(NO3)2}}. At 80 °C the hydrates convert to "basic copper nitrate", {{chem2|Cu2(NO3)(OH)3}}, which converts to {{chem2|CuO}} at 180 °C. Exploiting this reactivity, copper nitrate can be used to generate nitric acid by heating it until decomposition and passing the fumes directly into water. This method is similar to the last step in the Ostwald process. The equations are as follows:

:{{chem2|2 Cu(NO3)2 -> 2 CuO + 4 NO2 + O2}}

:{{chem2|3 NO2 + H2O -> 2 HNO3 + NO}}

Treatment of copper(II) nitrate solutions with triphenylphosphine, triphenylarsine, and triphenylstibine gives the corresponding copper(I) complexes {{chem2|[Cu(EPh3)3]NO3}} (E = P, As, Sb; Ph = {{chem2|C6H5}}). The group V ligand is oxidized to the oxide.{{cite book |last1=Gysling |first1=Henry J. |title=Inorganic Syntheses |series=Inorganic Syntheses |year=1979 |volume=19 |pages=92–97 |chapter=Coordination Complexes of Copper(I) Nitrate |doi=10.1002/9780470132500.ch19 |isbn=9780470132500}}

Anhydrous {{chem2|Cu(NO3)2}} is one of the few anhydrous transition metal nitrates.{{cite journal |doi=10.1039/qr9712500289 |title=Structural Aspects of Co-ordinated Nitrate Groups |year=1971 |last1=Addison |first1=C. C. |last2=Logan |first2=N. |last3=Wallwork |first3=S. C. |last4=Garner |first4=C. D. |journal=Quarterly Reviews, Chemical Society |volume=25 |issue=2 |page=289}} It cannot be prepared by reactions containing or producing water. Instead, anhydrous {{chem2|Cu(NO3)2}} forms when copper metal is treated with dinitrogen tetroxide:

:{{chem2|Cu + 2 N2O4 -> Cu(NO3)2 + 2 NO}}

File:Copper(II)-nitrate-monomer-2D-dimensions.png

Two polymorphs of anhydrous copper(II) nitrate, α and β, are known. Both polymorphs are three-dimensional coordination polymer networks with infinite chains of copper(II) centers and nitrate groups. The α form has only one Cu environment, with [4+1] coordination,{{cite journal |last1=Wallwork |first1=S. C. |last2=Addison |first2=W. E. |year=1965 |title=526. The crystal structures of anhydrous nitrates and their complexes. Part I. The α form of copper(II) nitrate |journal=J. Chem. Soc. |volume=1965 |pages=2925–2933 |doi=10.1039/JR9650002925}} but the β form has two different copper centers, one with [4+1] and one that is square planar.{{cite journal |last1=Troyanov |first1=S. I. |last2=Morozov |first2=I. V. |last3=Znamenkov |first3=K. O. |last4=Yu |last5=Korenev |first5=M. |year=1995 |title=Synthesis and X-Ray Structure of New Copper(II) Nitrates: Cu(NO₃)₂·H₂O and β-modification of Cu(NO₃)₂ |journal=Z. Anorg. Allg. Chem. |volume=621 |issue=7 |pages=1261–1265 |doi=10.1002/zaac.19956210727}}

The nitromethane solvate also features "[4+1] coordination", with four short Cu-O bonds of approximately 200 pm and one longer bond at 240 pm.{{cite journal |last1=Duffin |first1=B. |last2=Wallwork |first2=S. C. |year=1966 |title=The crystal structure of anhydrous nitrates and their complexes. II. The 1:1 copper(II) nitrate-nitromethane complex |journal=Acta Crystallographica |volume=20 |issue=2 |pages=210–213 |doi=10.1107/S0365110X66000434 |doi-access=}}

Heating solid anhydrous copper(II) nitrate under a vacuum to 150-200 °C leads to sublimation and "cracking" to give a vapour of monomeric copper(II) nitrate molecules.{{ cite journal | title = 628. The vapour pressure of anhydrous copper nitrate, and its molecular weight in the vapour state | first1 = C. C. | last1 = Addison | first2 = B. J. | last2 = Hathaway | journal = J. Chem. Soc. | year = 1958 | pages = 3099-3106 | doi = 10.1039/JR9580003099 }} In the vapour phase, the molecule features two bidentate nitrate ligands.{{cite journal |last1=LaVilla |first1=R. E. |last2=Bauer |first2=S. H. |year=1963 |title=The Structure of Gaseous Copper(II) Nitrate as Determined by Electron Diffraction |journal=J. Am. Chem. Soc. |volume=85 |issue=22 |pages=3597–3600 |doi=10.1021/ja00905a015}}

Five hydrates have been reported: the monohydrate ({{chem2|Cu(NO3)2*2H2O}}), the sesquihydrate ({{chem2|Cu(NO3)2*1.5H2O}}),{{cite journal |last1=Dornberger-Schiff |first1=K. |last2=Leciejewicz |first2=J. |year=1958 |title=Zur Struktur des Kupfernitrates Cu(NO₃)₂^.1.5H₂O |journal=Acta Crystallogr |volume=11 |issue=11 |pages=825–826 |doi=10.1107/S0365110X58002322 |doi-access=}} the hemipentahydrate ({{chem2|Cu(NO3)2*2.5H2O}}),{{cite journal |last1=Morosin |first1=B. |year=1970 |title=The crystal structure of Cu(NO₃)₂.2.5H₂O |journal=Acta Crystallographica Section B |volume=26 |issue=9 |pages=1203–1208 |doi=10.1107/S0567740870003898}} a trihydrate ({{chem2|Cu(NO3)2*3H2O}}),J. Garaj, Sbornik Prac. Chem.-Technol. Fak. Svst., Cskosl. 1966, pp. 35–39. and a hexahydrate ({{chem2|[Cu(OH2)6](NO3)2}}.{{cite journal |last1=Zibaseresht |first1=R. |last2=Hartshorn |first2=R. M. |year=2006 |title=Hexaaquacopper(II) dinitrate: absence of Jahn-Teller distortion |journal=Acta Crystallographica Section E |volume=62 |pages=i19–i22 |doi=10.1107/S1600536805041851}} The crystal structure of the hexahydrate appeared to show six almost equal Cu–O distances, not revealing the usual effect of a Jahn-Teller distortion that is otherwise characteristic of octahedral Cu(II) complexes. This non-effect was attributed to the strong hydrogen bonding that limits the elasticity of the Cu-O bonds but it is probably due to nickel being misidentified as copper in the refinement.

Copper(II) nitrate finds a variety of applications, the main one being its conversion to copper(II) oxide, which is used as catalyst for a variety of processes in organic chemistry. Its solutions are used in textiles and polishing agents for other metals. Copper nitrates are found in some pyrotechnics.H.Wayne Richardson "Copper Compounds" Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a07_567}}. It is often used in school laboratories to demonstrate chemical voltaic cell reactions. It is a component in some ceramic glazes and metal patinas.

Copper nitrate, in combination with acetic anhydride, is an effective reagent for nitration of aromatic compounds, known as the Menke nitration.{{cite journal |author=Menke J.B. |title=Nitration with nitrates |journal=Recueil des Travaux Chimiques des Pays-Bas |volume=44 |year=1925 |pages=141 |doi=10.1002/recl.19250440209}}

Hydrated copper nitrate adsorbed onto clay affords a reagent called "Claycop". The resulting blue-colored clay is used as a slurry, for example for the oxidation of thiols to disulfides. Claycop is also used to convert dithioacetals to carbonyls.Balogh, M. "Copper(II) Nitrate–K10 Bentonite Clay" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X}}. A related reagent based on montmorillonite has proven useful for the nitration of aromatic compounds.{{cite journal |doi=10.1002/anie.199005351 |volume=29 |issue=5 |title=Clays Direct Aromatic Nitration |year=1990 |journal=Angewandte Chemie International Edition in English |pages=535–536 |last1=Collet |first1=Christine}}

Copper(II) nitrate may also be used for copper electrowinning on small scale with a ammonia (NH₃) as a byproduct.{{Cite journal |last=Oishi |first=Tetsuo |last2=Koyama |first2=Kazuya |last3=Konishi |first3=Hirokazu |last4=Tanaka |first4=Mikiya |last5=Lee |first5=Jae-Chun |date=November 2007 |title=Influence of ammonium salt on electrowinning of copper from ammoniacal alkaline solutions |url=https://linkinghub.elsevier.com/retrieve/pii/S001346860700802X |journal=Electrochimica Acta |language=en |volume=53 |issue=1 |pages=127–132 |doi=10.1016/j.electacta.2007.06.024|url-access=subscription }}

No mineral of the ideal {{chem2|Cu(NO3)}} formula, or the hydrates, are known. Likasite, {{chem2|Cu3(NO3)(OH)5*2H2O}} and buttgenbachite, {{chem2|Cu19(NO3)2(OH)32Cl4*2H2O}} are related minerals.{{Cite web |url=https://www.mindat.org/min2399.html |title=Likasite |website=www.mindat.org}}

{{anchor|gerhardtite}} Natural basic copper nitrates include the rare minerals gerhardtite and rouaite, both being polymorphs of {{chem2|Cu2(NO3)(OH)3}}.{{Cite web |url=https://www.mindat.org/min-1680.html |title=Gerhardtite |website=www.mindat.org}}{{Cite web |url=https://www.mindat.org/min-10588.html |title=Rouaite |website=www.mindat.org}}{{Cite web |url=https://www.ima-mineralogy.org/Minlist.htm |title=List of Minerals |date=21 March 2011 |website=www.ima-mineralogy.org |author=International Mineralogical Association}} A much more complex, basic, hydrated and chloride-bearing natural salt is buttgenbachite.{{Cite web |url=https://www.mindat.org/min811.html |title=Buttgenbachite |website=www.mindat.org}}

{{Reflist}}

{{Commons category|Copper(II) nitrate}}

• [https://web.archive.org/web/20130530211504/http://www.npi.gov.au/substances/copper/index.html National Pollutant Inventory – Copper and compounds fact sheet]
• [https://web.archive.org/web/20170905225218/https://www.cdc.gov/niosh/ipcsneng/neng0240.html ICSC Copper and compounds fact sheet]

{{Copper compounds}}

{{nitrates}}

Category:Copper(II) compounds

Category:Nitrates

Category:Pyrotechnic oxidizers

Category:Pyrotechnic colorants

Category:Oxidizing agents