View source for Chemistry:Copper(II) carbonate

{{short description|Chemical compound}}
{{chembox
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| Watchedfields  = changed
| verifiedrevid  = 
| ImageFile      = File:Copper(II)-carbonate-xtal-3x3x3-3D-sf.png
| ImageSize      = 
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| IUPACName      = Copper(II) carbonate
| OtherNames     = Cupric carbonate, neutral copper carbonate
| Section1       = {{Chembox Identifiers
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 
| SMILES = C(=O)([O-])[O-].[Cu+2]
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 9AOA5F11GJ
| EC_number = 214-671-4
| PubChem = 14452<!-- NOTE: the PubChem entry (like many others) has lots of basic carbonate stuff incorrectly assigned to neutral carbonate.-->
|  ChemSpiderID = 13799
|  StdInChI = 1S/CH2O3.Cu/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
|  StdInChIKey = GEZOTWYUIKXWOA-UHFFFAOYSA-L
| CASNo = 1184-64-1 <!-- NOT 12069-69-1 -->
| CASNo_Ref = {{cascite|correct|ECHA}}
| EINECS = 
| RTECS = 
}}
| Section2       = {{Chembox Properties
| Formula = CuCO<sub>3</sub>
| MolarMass = 123.5549
| Appearance = green or blue Powder<ref name="seidel"/>
| Density = <!--  g/cm<sup>3</sup> -->
| MeltingPtC = 
| BoilingPtC = 
| Solubility = insoluble in water {{Clarify|date=November 2022}}
| SolubleOther =  
| SolubilityProduct = 10<sup>−11.45 ± 0.10</sup> at 25&nbsp;°C.<ref name="grauer"/><ref name="reit81"/><ref name="reit80"/>
| BandGap = <!-- [[Physics:Electronvolt|eV]] -->
| pKa = 
| pKb = 
| RefractIndex = 
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| Section3       = {{Chembox Structure
| CrystalStruct = 
| SpaceGroup = Pa-C<sup>2</sup><sub>s</sub> (7)  <ref name="seidel"/>
| LattConst_a = 6.092 Å
| LattConst_b = 4.493 Å
| LattConst_c = 7.030 Å
| LattConst_beta = 101,34°
| Coordination = 5 <ref name="seidel"/>
}}
| Section4       = {{Chembox Thermochemistry
| DeltaHf = <!-- kJ/mol -->
| Entropy = <!-- J/mol<sup>/K -->
 }}
| Section7       = {{Chembox Hazards
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| FlashPt = Non-flammable
| PEL = 
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}}
| Section8       = {{Chembox Related
| OtherAnions = [[Chemistry:Copper(II) sulfate|Copper(II) sulfate]]
| OtherCations = [[Chemistry:Nickel(II) carbonate|Nickel(II) carbonate]]<br/>[[Chemistry:Zinc carbonate|Zinc carbonate]]
| OtherFunction = 
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| OtherCompounds = 
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}}
'''Copper(II) carbonate''' or '''cupric carbonate''' is a [[Chemistry:Chemical compound|chemical compound]] with formula {{chem|Cu|C|O|3}}. At ambient temperatures, it is an [[Physics:Ionic compound|ionic solid]] (a [[Chemistry:Salt|salt]]) consisting of [[Chemistry:Copper|copper]](II) cations {{chem|Cu|2+}} and [[Chemistry:Carbonate|carbonate]] anions {{chem|C|O|3|2-}}.

This compound is rarely encountered because it is difficult to prepare<ref name="grauer"/> and readily reacts with water moisture from the air. The terms "copper carbonate", "copper(II) carbonate", and "cupric carbonate" almost always refer (even in chemistry texts) to a [[Chemistry:Basic copper carbonate|basic copper carbonate]] (or copper(II) carbonate [[Chemistry:Hydroxide|hydroxide]]), such as {{chem|Cu|2}}({{chem|OH}})<sub>2</sub>{{chem|C|O|3}} (which occurs naturally as the mineral [[Chemistry:Malachite|malachite]]) or {{chem|Cu|3}}({{chem|OH}})<sub>2</sub>({{chem|C|O|3}})<sub>2</sub> ([[Chemistry:Azurite|azurite]]).  For this reason, the qualifier '''neutral''' may be used instead of "basic" to refer specifically to {{chem|Cu|C|O|3}}.

==Preparation==

Reactions that may be expected to yield {{chem|Cu|C|O|3}}, such as mixing solutions of [[Chemistry:Copper(II) sulfate|copper(II) sulfate]] {{chem|Cu|S|O|4}} and [[Chemistry:Sodium carbonate|sodium carbonate]] {{chem|Na|2|C|O|3}} in [[Standard conditions for temperature and pressure|ambient conditions]], yield instead a basic carbonate and {{chem|C|O|2}}, due to the great affinity of the {{chem|Cu|2+}} ion for the [[Chemistry:Hydroxide|hydroxide]] anion {{chem|H|O|-}}.<ref>{{Cite book|title=Principles of Corrosion Engineering and Corrosion Control|last=Ahmad|first=Zaki|date=2006|publisher=Butterworth-Heinemann|isbn=9780750659246|location=Oxford|pages=120–270}}</ref>

Thermal decomposition of the basic carbonate at atmospheric pressure yields [[Chemistry:Copper(II) oxide|copper(II) oxide]] {{chem|Cu|O}} rather than the carbonate.

In 1960, C. W. F. T. Pistorius claimed synthesis by heating basic copper carbonate at 180&nbsp;°C in an atmosphere of [[Chemistry:Carbon dioxide|carbon dioxide]] {{chem|C|O|2}} (450 [[Physics:Atmosphere (unit)|atm]]) and water (50 atm) for 36 hours. The bulk of the products was well-crystallized malachite {{chem|Cu|2|C|O|3}}({{chem|O|H}})<sub>2</sub>, but a small yield of a rhombohedral substance was also obtained, claimed to be {{chem|Cu|C|O|3}}.<ref name="pistorius"/> However, this synthesis was apparently not reproduced.<ref name="grauer"/>

Reliable synthesis of true copper(II) carbonate was reported for the first time in 1973 by Hartmut Ehrhardt and others. The compound was obtained as a gray powder, by heating basic copper carbonate in an atmosphere of carbon dioxide (produced by the decomposition of [[Chemistry:Silver oxalate|silver oxalate]] {{chem|Ag|2|C|2|O|4}}) at 500&nbsp;°C and 2 G[[Pascal (unit)|Pa]] (20,000 atm).  The compound was determined to have a [[Physics:Monoclinic crystal system|monoclinic]] structure.<ref name="erhardt"/>

==Chemical and physical properties==
The stability of dry {{chem|Cu|C|O|3}} depends critically on the partial pressure of carbon dioxide (p<sub>CO<sub>2</sub></sub>).  It is stable for months in dry air, but decomposes slowly into {{chem|Cu|O}} and {{chem|C|O|2}} if p<sub>CO<sub>2</sub></sub> is less than 0.11 atm.<ref name="reit81"/>

In the presence of water or moist air at 25&nbsp;°C, {{chem|Cu|C|O|3}} is stable only for p<sub>CO<sub>2</sub></sub> above 4.57 atmospheres and pH between about 4 and 8.<ref name="gams"/> Below that partial pressure, it reacts with water to form a basic carbonate ([[Chemistry:Azurite|azurite]], {{chem|Cu|3}}({{chem|C|O|3}})<sub>2</sub>({{chem|OH}})<sub>2</sub>).<ref name="reit81"/>

:3 {{chem|Cu|C|O|3}} + {{chem|H|2|O}}  →  {{chem|Cu|3|(|C|O|3|)|2||(|O|H|)|2|}} + {{chem|C|O|2}}

In highly basic solutions, the complex anion {{chem|Cu(CO|3|)|2|2-}} is formed instead.<ref name="reit81"/>

The solubility product of the true copper(II) carbonate was measured by Reiterer and others as pK<sub>so</sub> = 11.45 ± 0.10 at 25&nbsp;°C.<ref name="grauer"/><ref name="reit81"/><ref name="reit80"/>

==Structure==
In the [[Chemistry:Crystal structure|crystal structure]] of CuCO<sub>3</sub>, copper adopts a distorted [[Physics:Square pyramidal molecular geometry|square pyramidal]] coordination environment with [[Physics:Coordination number|coordination number]] 5. Each [[Chemistry:Carbonate|carbonate]] ion bonds to 5 copper centres.<ref name="seidel"/>

<gallery>
File:Copper(II)-carbonate-unit-cell-3D-bs-N17-M25.png|[[Unit cell]] of CuCO<sub>3</sub>
File:Copper(II)-carbonate-xtal-Cu-coordination-3D-bs-N17-M25.png|Copper coordination environment
File:Copper(II)-carbonate-xtal-carbonate-coordination-3D-bs-N17-M25.png|Carbonate coordination environment
</gallery>

==References==

<references>

<ref name="grauer">Rolf Grauer (1999) "[http://www.nagra.ch/data/documents/database/dokumente/$default/Default%20Folder/Publikationen/NTBs%201994-2000/e_ntb99-03.pdf Solubility Products of M(II) Carbonates] {{Webarchive|url=https://web.archive.org/web/20181101005235/https://www.nagra.ch/data/documents/database/dokumente/%24default/Default%20Folder/Publikationen/NTBs%201994-2000/e_ntb99-03.pdf |date=2018-11-01 }}". Technical Report NTB-99-03, NAGRA - National Cooperative for the Disposal of Radioactive Waste; pages 8, 14, and 17. Translated by U. Berner.</ref>

<ref name="erhardt">Hartmut Erhardt, Wilhelm Johannes, and Hinrich Seidel (1973): "Hochdrucksynthese von Kupfer(II)-Carbonat", Z. Naturforsch., volume 28b, issue 9-10, page 682. {{doi|10.1515/znb-1973-9-1021}}</ref>

<ref name="seidel">H. Seidel, H. Ehrhardt,  K. Viswanathan,  W. Johannes (1974): "Darstellung, Struktur und Eigenschaften von Kupfer(II)-Carbonat". Z. anorg. allg. Chem., volume 410, pages 138-148.  {{doi|10.1002/zaac.19744100207}}</ref>

<ref name="pistorius">C. W. F. T. Pistorius (1960): "Synthesis at High Pressure and Lattice Constants of Normal Cupric Carbonate". Experientia, volume XVI, page 447-448.  {{doi|10.1007/BF02171142}}</ref>

<ref name="reit80">F. Reiterer (1980): "Löslichkeitskonstanten und Freie Bildungsenthalpien neutraler Übergangsmetallcarbonate". Thesis, Montanuniversität Leoben.</ref>

<ref name="reit81">F. Reiterer, W. Johannes, H. Gamsjäger (1981): "Semimicro Determination of Solubility Constants: Copper(II) Carbonate and Iron(II) Carbonate". Mikrochim. Acta, volume 1981, page 63.  {{doi|10.1007/BF01198705}}</ref>

<ref name="gams">H. Gamsjäger and W. Preis (1999): "Copper Content in Synthetic Copper Carbonate." Letter to J. Chem. Educ., volume 76, issue 10, page 1339. {{doi|10.1021/ed076p1339.1}}</ref>

</references>

{{carbonates}}
{{hydroxides}}
{{copper compounds}}

[[Category:Copper(II) compounds]]
[[Category:Carbonates]]

{{Sourceattribution|Copper(II) carbonate}}