15
$\begingroup$

In qualitative analysis, $\ce{NH4+}$ ions are confirmed using Nessler's reagent:-

$$\ce{NH4+ + 2[HgI4]^{2−} + 4OH− → HgO·Hg(NH2)I ↓ + 7I^{−} + 3H2O}$$

The brown precipitate formed is called iodide of Millon's base. It is also written as $\ce{3HgO.Hg(NH3)2I2}$ and as $\ce{NH2.Hg2I3}$. (wikipedia).

But its structure is present differently in different sites:-

  1. Source 1 - ionic form

  1. Source 2 - Here the reaction is given differently:-

$$\ce{([K2]HgI4 <=> 2KI + HgI2) * 2}$$ $$\ce{HgI2 + NH3 -> Hg[NH2]I + NH4I}$$ $$\ce{Hg[NH2]I + HgI2 -> NH2Hg2I3 }$$ $$\ce{[K2]HgI4 + 2NH3 -> NH2Hg2I3 + 4KI + KH4I }$$

structure -

enter image description here

  1. Source 3- non ionic form

enter image description here

  1. Source 4 - Hydrate form; Here also the reaction is different:- $$\ce{[K2]HgI4 -> 2KI + HgI2}$$ $$\ce{HgI2 + NH3 -> Hg[NH2]I + HI}$$ enter image description here

This site also says that its structure is still uncertain. Various other structure has been proposed:-

enter image description here

So, what is the correct reaction, correct formula and correct structure of iodide of Millon's base?

$\endgroup$
3
  • $\begingroup$ @permeakra, the paper showed the structure of millon base. Not the iodide of millon's base. $\endgroup$ Jan 11, 2016 at 12:07
  • $\begingroup$ the second link provides structure for similar compounds, chloride of milton's base . It should give an idea, I believe. Anyway, it is absolutely clear, that non of structures provided in the question has anything to do with real life: the iodide is definitely polymeric. $\endgroup$
    – permeakra
    Jan 11, 2016 at 16:58

1 Answer 1

6
+50
$\begingroup$

First, ignore any monomeric formula. The compound is definitely polymeric.

The literature contains hints for existence of two separate lines of compounds. The first one is salts of polyamidomercury: $\ce{[Hg(NH2)]_{n}A_{n}}${1} with mercury-amide chains in the structure, and $\ce{(Hg2N)_{n}A_{n}}$ with structure based on crystoballite {2}{3}

It seems thatn the lines are not distinguished in earlier literature, but recent researchers use the words "Millon's base salts" for $\ce{(Hg2N)_{n}A_{n}}$ only.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.