Editing Mercury(II) oxide (section)

==Synthesis and reactions==
[[File:Montroydite.jpg|thumb|left|Montroydite structure (red atoms are oxygen)]]
[[File:Cinnabar structure.jpg|thumb|left|[[Cinnabar]] structure]]

The red form of HgO can be made by heating Hg in oxygen at roughly 350&nbsp;°C, or by [[pyrolysis]] of [[mercury(II) nitrate|Hg(NO<sub>3</sub>)<sub>2</sub>]].<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> The yellow form can be obtained by precipitation of aqueous Hg<sup>2+</sup> with alkali.<ref name = "Greenwood"/> The difference in color is due to particle size; both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an Hg-O-Hg angle of 108°.<ref name = "Greenwood"/>

HgO is soluble in many conventional strong acids through protonation of the anion.<ref>{{cite web |title=Characteristic Reactions of Mercury Ions (Hg²⁺ and Hg₂²⁺) |url=https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Qualitative_Analysis/Characteristic_Reactions_of_Select_Metal_Ions/Characteristic_Reactions_of_Mercury_Ions_(Hg_and_Hg) |website=LibreTextsChemistry |access-date=23 July 2024}}</ref> The exceptions include acids which form insoluble mercury(II) salts, like [[mercury(II) iodide]] in the case of [[hydroiodic acid]]. Dissolution is also possible through complexation of the cation; e.g. cyanide ligands form stable water soluble mercury(II) complexes.