Copper(I) iodide

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Copper(I) iodide
Copper(I) iodide
Identifiers
CAS number7681-65-4 YesY
PubChem24350
ChemSpider22766 YesY
Jmol-3D imagesImage 1
Properties
Molecular formulaCuI
Molar mass190.45 g/mol
AppearanceWhite powder
when impure: tan or brownish
Odorodorless
Density5.67 g/cm3 [1]
Melting point606 °C (1,123 °F; 879 K)
Boiling point1,290 °C (2,350 °F; 1,560 K) (decomposes)
Solubility in water0.0042 g/100 mL
Solubility product, Ksp1 x 10−12 [2]
Solubilitysoluble in ammonia and potassium solutions
Refractive index (nD)2.35
Structure
Crystal structurezincblende
Coordination
geometry
Tetrahedral anions and cations
Hazards
MSDSSigma Aldrich[3]
GHS pictogramsGHS-pictogram-exclam.svgGHS-pictogram-pollu.svg
GHS hazard statementsH302, H315, H319, H335, H400, H410
GHS precautionary statementsP261, P273, P305+351+338, P501
EU IndexNot listed
NFPA 704
Flash pointNon-flammable
Related compounds
Other anionsCopper(I) fluoride
Copper(I) chloride
Copper(I) bromide
Other cationssilver(I) iodide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references
 
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Copper(I) iodide
Copper(I) iodide
Identifiers
CAS number7681-65-4 YesY
PubChem24350
ChemSpider22766 YesY
Jmol-3D imagesImage 1
Properties
Molecular formulaCuI
Molar mass190.45 g/mol
AppearanceWhite powder
when impure: tan or brownish
Odorodorless
Density5.67 g/cm3 [1]
Melting point606 °C (1,123 °F; 879 K)
Boiling point1,290 °C (2,350 °F; 1,560 K) (decomposes)
Solubility in water0.0042 g/100 mL
Solubility product, Ksp1 x 10−12 [2]
Solubilitysoluble in ammonia and potassium solutions
Refractive index (nD)2.35
Structure
Crystal structurezincblende
Coordination
geometry
Tetrahedral anions and cations
Hazards
MSDSSigma Aldrich[3]
GHS pictogramsGHS-pictogram-exclam.svgGHS-pictogram-pollu.svg
GHS hazard statementsH302, H315, H319, H335, H400, H410
GHS precautionary statementsP261, P273, P305+351+338, P501
EU IndexNot listed
NFPA 704
Flash pointNon-flammable
Related compounds
Other anionsCopper(I) fluoride
Copper(I) chloride
Copper(I) bromide
Other cationssilver(I) iodide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references


Copper(I) iodide is the inorganic compound with the formula CuI. It is also known as cuprous iodide. It is useful in a variety of applications ranging from organic synthesis to cloud seeding.

Pure copper(I) iodide is white, but samples are often tan or even, when found in nature as rare mineral marshite, reddish brown, but such colour is due to the presence of impurities. It is common for samples of iodide-containing compounds to become discolored due to the facile aerobic oxidation of the iodide anion to molecular iodine.[4]

Structure[edit]

Copper(I) iodide, like most "binary" (containing only two elements) metal halides, is an inorganic polymer. It has a rich phase diagram, meaning that it exists in several crystalline forms. It adopts a zinc blende structure below 390 °C (γ-CuI), a wurtzite structure between 390 and 440 °C (β-CuI), and a rock salt structure above 440 °C (α-CuI). The ions are tetrahedrally coordinated when in the zinc blende or the wurtzite structure, with a Cu-I distance of 2.338 Å. Copper(I) bromide and copper(I) chloride also transform from the zinc blende structure to the wurtzite structure at 405 and 435 °C, respectively. Therefore, the longer the copper – halide bond length, the lower the temperature needs to be to change the structure from the zinc blende structure to the wurtzite structure. The interatomic distances in copper(I) bromide and copper(I) chloride are 2.173 and 2.051 Å, respectively.[5]

Copper(I)-iodide-unit-cell-3D-balls.png
Copper(I)-iodide-(beta)-unit-cell-3D-balls.png
Copper(I)-iodide-(alpha)-unit-cell-3D-balls.png
γ-CuI
β-CuI
α-CuI

Preparation[edit]

Copper(I) iodide can be prepared by heating iodine and copper in concentrated hydriodic acid, HI. In the laboratory however, copper(I) iodide is prepared by simply mixing an aqueous solution of sodium or potassium iodide and a soluble copper(II) salt such copper sulfate.

Cu2+ + 2I → CuI2

The CuI2 immediately decomposes to iodine and insoluble copper(I) iodide, releasing I2.[6]

2 CuI2 → 2 CuI + I2

This reaction has been employed as a means of assaying copper(II) samples, since the evolved I2 can be analyzed by redox titration. The reaction in itself may look rather odd, as using the rule of thumb for a proceeding redox reaction, Eooxidator − Eoreductor > 0, this reaction fails. The quantity is below zero, so the reaction should not proceed. But the equilibrium constant[7] for the reaction is 1.38*10−13. By using fairly moderate concentrates of 0.1 mol/L for both iodide and Cu2+, the concentration of Cu+ is calculated as 3*10−7. As a consequence, the product of the concentrations is far in excess of the solubility product, so copper(I)iodide precipitates. The process of precipitation lowers the copper(I) concentration, providing an entropic driving force according to Le Chatelier's principle, and allowing the redox reaction to proceed.

CuI is poorly soluble in water (0.00042 g/L at 25 °C), but it dissolves in the presence of NaI or KI to give the linear anion [CuI2]. Dilution of such solutions with water reprecipitates CuI. This dissolution–precipitation process is employed to purify CuI, affording colorless samples.[4]

Uses[edit]

CuI has several uses:

References[edit]

  1. ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3. 
  2. ^ Skoog West Holler Crouch. Fundamentals of Inorganic Chemistry. Brooks/Cole, 2004, pp. A-6 ISBN 978-0-03-035523-3
  3. ^ Sigma-Aldrich Co., Copper(I) iodaide. Retrieved on 2014-09-09.
  4. ^ a b Kauffman, G. B.; Fang, L. Y. (1983). "Purification of Copper(I) Iodide". Inorg. Synth. Inorganic Syntheses 22: 101–103. doi:10.1002/9780470132531.ch20. ISBN 978-0-470-13253-1. 
  5. ^ Wells, A. F. Structural Inorganic Chemistry Oxford University Press, Oxford, (1984). 5th ed., p. 410 and 444.
  6. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  7. ^ The value depends on the specific half-reaction for iodine. The value itself is calculated by using the formula: Kredox=10^{(nox*nred/0.0591)*(Eooxidator − Eoreductor)} which in itself is easily derived from the Nernst equations for the specific half reactions. Using Eoox=EoCu2+/Cu+ = 0.15; nox = 1 for copper; Eored=EoI/I2 = 0.52; nred = 2 for iodine
  8. ^ Klapars, A.; Buchwald, S. L. (2002). "Copper-Catalyzed Halogen Exchange in Aryl Halides: an Aromatic Finkelstein Reaction". J. Am. Chem. Soc. 124 (50): 14845. doi:10.1021/ja028865v. PMID 12475315. 
  9. ^ Marshall, J. A.; Sehon, C. A., Isomerization of Β-Alkynyl Allylic Alcohols to Furans Catalyzed by Silver Nitrate on Silica Gel: 2-Pentyl-3-methyl-5-heptylfuran, Org. Synth. 76: 263 
  10. ^ a b H. W. Richardson "Copper Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a07 567

Sources[edit]

External links[edit]