What is the structure of iodide of Millon's base? 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:-


Source 1 - ionic form





Source 2  - Here the reaction is given differently:-


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

structure - 




Source 3- non ionic form





Source 4 - Hydrate form; Here also the reaction is different:-
$$\ce{[K2]HgI4 -&gt; 2KI + HgI2}$$
$$\ce{HgI2 + NH3 -&gt; Hg[NH2]I + HI}$$



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



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