MadSci Network: Chemistry

Re: Reaction between tin and iodine

Date: Mon Aug 17 10:02:00 1998
Posted By: Henry Boyter, Senior Scientist
Area of science: Chemistry
ID: 901934148.Ch

Because you only mention tin without the form, I will deal with the 
reaction of iodine with tin metal.  I looked in several inorganic 
chemistry books and found various levels of information.  From "Chemistry 
of the Elements" by Greenwood and Earnshaw (Leeds), supplied some of the 
following information.

To produce SnI2 in anhydrous form, react Sn metal (hot) with I2 at 
elevated temperatures.  No water is used.  Also and better, Sn and I2 
(excess) can be reacted in a solution of hydrochloric acid to give SnI2.  
If Sn and I2 are reacted in caustic water, hydrates and hydroxides are 
formed.  The reaction should be done in acid solution, since Sn(OH)x can 
be formed easily in basic solutions.

SnI4 can also be formed if the +4 oxidation form of the metal is used.  
This is the more common form of Sn iodide and can be formed from the 
reaction of SnCl4 with I2 or I- (excess).

The Sn iodides have the ability of forming molecular polymer structures 
where one iodide bridges between the Sn.  These would be structures like 
Sn2I3, etc, with larger structure predominating.  THe SnI4's do this also.

The mechanisms for these reactions will vary.  For the anhydrous reaction 
(no water), the reduction of the iodine and the oxidation of the tin will 
be a surface phenomenon with the I2 bonding both atoms to the surface.  It 
could also be a single atom attachment with a more complicated mechanism 
involving iodine radicals.  This mechanism has probably been delineated, 
but would take some library time to find the information.  In acid, the 
mechanism will be similar, except that the oxidized tin (Sn+2) and iodide 
(I-) may react away from the surface of the metal.  For example, electron 
transfer could take place on the surface, and formation of SnI2 could take 
place away from the surface (but near) in the form of hydrated atoms.

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