Mercury iodide, Hgl

Hgili(g) Mercury iodide (Hgl) 1322 IgPbjCcr.l) Lead iodide (Pbl2)... 

Mercury iodide process. The removal of mercury from the acid can be performed using potassium iodide (KI), which is added to the acid, which should be at least 93 wt.% H,SO, at a temperature of about 0°C, and insoluble mercuric iodide (Hgl,) is precipitated. 

P. Lemoult obtained phosphorus trisiodomercuriate, P(HgI)8, by the action of phosphine, diluted with hydrogen or carbon dioxide, on a dil, soln. of potassium iodomercuriate. The product is washed and dried in vacuo. It is slowly decomposed by warm water and rapidly by alkali-lye. Nitric acid and aqua regia decompose it violently. F. Venturoli prepared "yellow phosphorus iodobisiodo-mercuriate, I.P (Hgl)2, by the action of phosphorus on an alcoholic soln. of potassium iodide. The product is decomposed by heat into phosphorus, and mercurous and mercuric iodides. 

Methylene iodide, on the other hand, when left in contact with metallic mercury and some mercurous iodide in a sealed tube for four or five days, combines with the mercury. Two products are produced, but no gas is evolved when the tube is opened. The first compound crystallises from boiling alcohol in slender, wdiite needles it is best purified by solution in methylene iodide and precipitation with ether, and is insoluble in the usual solvents. Sakurai assigned the formula I-CHg -Hgl to the substance. This monomercuric methylene iodide or iodomethyl mercuric iodide when heated with iodine in potassium iodide solution yields methylene iodide and mercuric iodide, and similar decomposition takes place with chlorine or bromine. 

Addition of excess iodide to the insoluble Hgl2 results in the formation of soluble mercury iodo complex [Hgl3], with a trigonal planar structure. The ion is solvated in water and converts to a tetrahedral structure. Further, addition of I leads to tetrahedral [Hgl ] ". Reaction of iodide salts with Hg° can be used to produce mercury iodo complexes. Other halide and pseudohalides also form [HgXj] and [HgX4]. The tetrahalo anions (seeAniod) are usually tetrahedral, while the trihalo ions readily add solvent molecules to form distorted tetrahedral or Trigonal Bipyramidal structures. 

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