Mercury(I) nitrate is an inorganic compound, a salt of mercury and nitric acid with the formula Hg<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>. A yellow solid, the compound is used as a precursor to other Hg<sub>2</sub><sup>2+</sup> complexes. The structure of the hydrate has been determined by X-ray crystallography. It consists of a [H<sub>2</sub>O-Hg-Hg-OH<sub>2</sub>]<sup>2+</sup> center, with a Hg-Hg distance of 254 pm.
It was first mentioned by Indian chemist Acharya Prafulla Chandra Ray in 1896.
Mercury(I) nitrate is formed when elemental mercury is combined with dilute nitric acid (concentrated nitric acid will yield mercury(II) nitrate). Mercury(I) nitrate is a reducing agent which is oxidized upon contact with air.
Mercuric(II) nitrate reacts with elemental mercury(0) to form mercurous(I) nitrate (comproportionation reaction):
Solutions of mercury(I) nitrate are acidic due to slow reaction with water:
Hg<sub>2</sub>(NO<sub>3</sub>)(OH) forms a yellow precipitate.
If the solution is boiled, or exposed to light, mercury(I) nitrate undergoes a disproportionation reaction yielding elemental mercury and mercury(II) nitrate:
These reactions are reversible; the nitric acid formed can redissolve the basic salt.