Copper (I) iodide

Crystal structure
__ Cu +      __ I -
General
Surname	Copper (I) iodide
other names	Copper iodine
Ratio formula	CuI
Brief description	pure white crystal powder
External identifiers / databases
CAS number 7681-65-4 EC number 231-674-6 ECHA InfoCard 100,028,795 PubChem 24350 ChemSpider 22766 Wikidata Q411207
properties
Molar mass	190.44 g · mol -1
Physical state	firmly
density	5.62 g cm −3 (20 ° C)
Melting point	588 ° C
boiling point	1290 ° C
Vapor pressure	13.3 h Pa at 656 ° C
solubility	practically insoluble in water
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 302-315-317-318-335-410 P: 280-301 + 312 + 330-305 + 351 + 338
MAK	0.1 mg m −3
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Copper (I) iodide is the copper salt of hydriodic acid . In a completely pure state, it is a white powder.

properties

Because of the electron configuration d ¹⁰ , copper (I) compounds are diamagnetic . Copper iodide crystallizes in the sphalerite structure . It is significantly less sensitive to light than copper (I) bromide and copper (I) chloride , but still releases small amounts of iodine under the influence of light in the room air with slight decomposition. With a solubility of 0.00042 g / l at 25 ° C, the compound is practically insoluble in water.

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structure

Copper (I) iodide has a complex phase diagram showing the existence of multiple crystalline forms. It is tetrahedrally coordinated when it is in the zinc blende structure, in which it crystallizes below 300 ° C. The atomic distance between the copper and iodine atoms is 2.338 Å .

Extraction and presentation

In the laboratory, copper (I) iodide can be produced by dissolving copper in concentrated hydriodic acid , reacting copper (I) cyanide with hydrogen iodide or by mixing a copper (II) salt (usually a copper sulfate solution ) and a potassium iodide solution.

The last variant in particular can be used in the form of titrating a copper (II) sulfate solution with a stoichiometric solution of potassium iodide and sodium thiosulfate in order to obtain the cleanest possible product:

${\displaystyle {\ce {2 CuSO4 + 4 KI -> 2 CuI2 + 2 K2SO4}}}$

${\displaystyle {\ce {2 CuI2 -> 2 CuI + I2}}}$

${\displaystyle {\ce {2 Na2S2O3 + I2 -> Na2S4O6 + 2 NaI}}}$

The intermediate copper (II) iodide is unstable and breaks down almost instantly into the copper (I) iodide and free iodine. This decay forms the basis for the iodometric determination of copper. However, since this iodine tends to contaminate the product obtained in excess and form soluble copper iodide complexes, it is removed from the reaction by the thiosulfate used and the overall equation is obtained:

${\displaystyle {\ce {2 CuSO4 + 4 KI + 2 Na2S2O3 -> 2 CuI + 2 K2SO4 + Na2S4O6 + 2 NaI}}}$

In industrial production, iodine vapor is directed onto copper metal:

${\displaystyle {\ce {2 Cu + I2 ->[T][]2 CuI}}}$

Individual evidence

1. ↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 976.
2. ↑ ^{a b c d e f g h} Entry on copper (I) iodide in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
3. ↑ Entry on copper iodides. In: Römpp Online . Georg Thieme Verlag, accessed on June 7, 2014.
4. ^ Erwin Riedel, "Inorganische Chemie", 4th edition, de Gruyter Verlag, ISBN 3-11-016602-X .
5. ^ ^{A b c} George B. Kauffmann and Robert P. Pinnell: Copper (I) iodide . In: Eugene G. Rochow (Ed.): Inorganic Syntheses . tape 6 . McGraw-Hill Book Company, Inc., 1960, pp. 3–6 (English).
6. ^ AF Wells: Structural Inorganic Chemistry . Oxford University Press, Oxford. 5th edition 1984, pp 410 and 444.