Mercury(I) nitrate

Mercury nitrate is an inorganic compound, a salt of mercury and nitric acid with the formula Hg₂₂. A yellow solid, the compound is used as a precursor to other Hg₂²⁺ complexes. The structure of the hydrate has been determined by X-ray crystallography. It consists of a ²⁺ center, with a Hg-Hg distance of 254 pm.
It was first mentioned by Indian chemist Acharya Prafulla Chandra Ray in 1896.

Reactions

Mercury nitrate is formed when elemental mercury is combined with dilute nitric acid. Mercury nitrate is a reducing agent which is oxidized upon contact with air.
Mercuric nitrate reacts with elemental mercury to form mercurous nitrate :
Solutions of mercury nitrate are acidic due to slow reaction with water:
Hg₂ forms a yellow precipitate.
If the solution is boiled, or exposed to light, mercury nitrate undergoes a disproportionation reaction yielding elemental mercury and mercury nitrate:
These reactions are reversible; the nitric acid formed can redissolve the basic salt.