[Biochislife]

Dear reader,

I hope you're having a great day all is sweet&shine. A couple of days ago I had a lab where we determined the %I in (Me₄N)I₃ and in (Me₄N)I₅ using gravimetric  analysis. The calculations where pretty straight forward although I was intrigued by the different colour displayed by both salts.

a) (Me₄N)I + I₂  (Me₄N)I₂

b) (Me₄N)I + 2I₂     (Me₄N)I₅

In both reactions the amount of  Iodide used was equivalent (0.2g) , only the iodine content differed (1.3g for a) and 2.6g for b)). The triiodide crystals displayed a magnificent shiny purple colour that soon turned into a reddish/bordeaux shade after being dried. The pentaiodide crystals displayed a rather unique colour between silver and blue.

I was therefore intrigued (and still am) by the visual difference between those two crystals. My primal hypothesis was that the I₅ structure brought delocalization in the proximity of the tetramethylammonium causing the molecule to absorb in the far-end of the visible spectrum. This is all of course highly speculative so I'd love to hear your point of view regarding that colour change  .