Mercury hydroxide or mercury dihydroxide is an inorganic metal hydroxide

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 with the chemical formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 HgH₂O₂ or more commonly written as Hg(OH)₂.

Synthesis

It is not possible to make the chemical by adding OH^- to Hg²⁺ in aqueous solution since this merely precipitates yellow solid HgO, although it is possible that Hg(OH)₂ is momentarily produced during the reaction.

The first experimental evidence for the existence of the molecule was reported by Wang and Andrews in 2004. They produced it by irradiating a frozen mixture of mercury, oxygen and hydrogen with light from a mercury arc lamp. The mixture had been produced by evaporating mercury atoms at 50 °C into a gas consisting of neon, argon or deuterium (in separate experiments) plus 2 to 8% hydrogen and 0.2 to 2.0% oxygen. The mixture was then condensed at 5 kelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

 onto a caesium iodide

Caesium iodide

Caesium iodide is an ionic compound often used as the input phosphor of an x-ray image intensifier tube found in fluoroscopy equipment....

window through which it could be irradiated.