Chemical of the Day - Copper iodide

Ok I shall start off with the chemical of the day then.
So today's chemical is copper (I) iodide.
Some may wonder why it is not copper (II) iodide which is usually the preferred oxidation state for copper.
Nvm wikipedia says nothing about why copper (I) iodide is more stable than copper (II) iodide. My guess would be due to steric strain between the iodide ion and copper ion, since iodine is much larger, so the ionic lattice would be strained.

Formula: CuI

Appearance: white powder (pure). brownish (impure)

Structure: Giant ionic lattice

Ksp: 1 x 10^-12

Preparation: Heating of iodine and copper in concentrated HI,
Addition of KI to a soluble copper salt such as CuSO4. The product formed is CuI2, which decomposes immediately to CuI and I2.
Hence if given an unknown X, which is mixed with KI and then CCl4 is added, if a purple layer is seen with a white powder, it can be quite confirmed that X contains Cu2+, since CuI2 decomposes immediately to give CuI (white powder) and I2 (dissolves to give purple colour in CCl4)

Uses: Organometallic coupling. CuI is one of the reagents required for the synthesis of the Gilman reagent. What this reagent can do is to replace the halide group on a haloalkane with another R group. It is prepared by reaction of an organolithium compound with CuI with diethyl ether as solvent.
2CH3Li + CuI -> (CH3)2CuLi + LiI
In this case the (CH3)2CuLi is the Gilman reagent. Of course the R group bonded to the copper can be changed to other substituent other than methyl group. Gilman reagent can react with haloalkanes as follows:
(CH3)2CuLi + CH3(CH2)8CH2I -> CH3(CH2)8CH2CH3 + LiI + CH3Cu
As can be seen from the reaction, one of the CH3 groups in the Gilman reagent substituted the I from the haloalkane forming a larger alkane as the main product. This reaction is useful as it forms a C-C bond, thereby making possible preparation of larger molecules from smaller ones. This is even more useful as you can use this reaction to add alkyl groups to a benzene compound as well.
C6H5I (iodobenzene) + (CH3)2CuLi -> C6H5CH3 (toluene) + CH3Cu + LiI.

Other info: Used for cloud seeding. Used to detect Hg, upon addition of CuI to Hg, copper tetraiodomercurate is formed which turns the white powder brown. Soluble in concentrated KI to give [CuI2]-

Now gc can go and do phenol. lol.