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Copper(I) iodide is white, but samples are often tan or even, when found in nature as mineral marshite, reddish brown, but such color is due to impurities. It is common for iodides to become discolored because of the easy oxidation of the iodide anion to iodine.
Additional recommended knowledge
In the laboratory, copper(I) Iodide is prepared by simply mixing an aqueous solutions of sodium or potassium iodide and a soluble copper(II) salt such copper sulfate.
The CuI2 immediately decomposes to iodine and insoluble copper(I) iodide, releasing I2.
This reaction has been employed as a means of assaying copper(II) samples, since the evolved I2 can be analyzed by redox titration. Copper(I) iodide can also prepared by heating iodine and copper in concentrated hydriodic acid, HI.
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.
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 (ɣ-CuI), a wurtzite structure between 390 and 440 °C (β-CuI), and a cubic 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.
CuI has several uses:
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Copper(I)_iodide". A list of authors is available in Wikipedia.|