Copper(II) carbonate or cupric carbonate is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...

with formula . At ambient temperatures, it is an ionic solid (a

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantiti ...

) consisting of copper(II)

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s . This compound is rarely encountered because it is difficult to prepare 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

basic copper carbonate Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound (a salt) consisting of the ions copper(II) , carbonate , and hydroxide . The name most commonly refers to the compound w ...

(or copper(II) carbonate

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

), such as ()₂ (which occurs naturally as the mineral

malachite Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures ...

) or ()₂()₂ (

azurite Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France. The mineral, a basic ca ...

). For this reason, the qualifier neutral may be used instead of "basic" to refer specifically to .

Preparation

Reactions that may be expected to yield , such as mixing solutions of

copper(II) sulfate Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered hy ...

and sodium carbonate in ambient conditions, yield instead a basic carbonate and , due to the great affinity of the ion for the

anion . Thermal decomposition of the basic carbonate at atmospheric pressure yields

copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite. It i ...

rather than the carbonate. In 1960, C. W. F. T. Pistorius claimed synthesis by heating basic copper carbonate at 180 °C in an atmosphere of carbon dioxide (450 atm) and water (50 atm) for 36 hours. The bulk of the products was well-crystallized malachite ()₂, but a small yield of a rhombohedral substance was also obtained, claimed to be . However, this synthesis was apparently not reproduced. 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

silver oxalate Silver oxalate () is commonly employed in experimental petrology to add carbon dioxide () to experiments as it will break down to silver (Ag) and carbon dioxide under geologic conditions. It is also a precursor to the production of silver nanopa ...

) at 500 °C and 2 G Pa (20,000 atm). The compound was determined to have a

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

structure.

Chemical and physical properties

The stability of dry depends critically on the partial pressure of carbon dioxide (p_CO₂). It is stable for months in dry air, but decomposes slowly into and if p_CO₂ is less than 0.11 atm. In the presence of water or moist air at 25 °C, is stable only for p_CO₂ above 4.57 atmospheres and pH between about 4 and 8. Below that partial pressure, it reacts with water to form a basic carbonate (

, ()₂()₂). :3 + → + In highly basic solutions, the complex anion ()₂²⁻ is formed instead. The solubility product of the true copper(II) carbonate was measured by Reiterer and others as pK_so = 11.45 ± 0.10 at 25 °C.

Structure

In the crystal structure of CuCO₃, copper adopts a distorted

square pyramidal In molecular geometry, square pyramidal geometry describes the shape of certain compounds with the formula where L is a ligand. If the ligand atoms were connected, the resulting shape would be that of a pyramid with a square base. The point ...

coordination environment with coordination number 5. Each

ion bonds to 5 copper centres. File:Copper(II)-carbonate-unit-cell-3D-bs-N17-M25.png,

Unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

of CuCO₃ 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

References

Rolf Grauer (1999)
Solubility Products of M(II) Carbonates
. Technical Report NTB-99-03, NAGRA - National Cooperative for the Disposal of Radioactive Waste; pages 8, 14, and 17. Translated by U. Berner. Hartmut Erhardt, Wilhelm Johannes, and Hinrich Seidel (1973): "Hochdrucksynthese von Kupfer(II)-Carbonat", Z. Naturforsch., volume 28b, issue 9-10, page 682. 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. C. W. F. T. Pistorius (1960): "Synthesis at High Pressure and Lattice Constants of Normal Cupric Carbonate". Experientia, volume XVI, page 447-448. F. Reiterer (1980): "Löslichkeitskonstanten und Freie Bildungsenthalpien neutraler Übergangsmetallcarbonate". Thesis, Montanuniversität Leoben. 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. H. Gamsjäger and W. Preis (1999): "Copper Content in Synthetic Copper Carbonate." Letter to J. Chem. Educ., volume 76, issue 10, page 1339. {{copper compounds Copper(II) compounds Carbonates