HgCl2
Mercury(II) chloride · mercuric chloride, corrosive sublimate, dichloromercury, mercury bichloride, mercury dichloride
HgCl2 is mercury(II) chloride, also known as mercuric chloride or corrosive sublimate. It is a molecular inorganic compound of mercury and chlorine in a one-to-two ratio. It forms a white, highly toxic crystalline solid made of packed, nearly linear Cl–Hg–Cl molecules, and it is a thermodynamically stable compound with a wide band gap that makes it an electrical insulator.
About Mercury(II) chloride
What is HgCl2 and what structure does it adopt?
Mercury(II) chloride is a binary halide of divalent mercury and chlorine. Many metal chlorides form extended ionic networks, but solid HgCl2 is a molecular crystal. It is built from discrete, nearly linear Cl–Hg–Cl units held together by weaker secondary contacts. This reflects how covalent the mercury–chlorine bond is and divalent mercury's typical preference for linear coordination. The crystal structure has been determined experimentally by diffraction.
What is HgCl2 used for?
Under the historical name corrosive sublimate, mercury(II) chloride was widely used as an antiseptic, disinfectant, wood preservative and photographic intensifier. It was also once a first-line treatment for syphilis. Its high toxicity now limits it to specialised uses. It serves as a laboratory reagent in synthetic and analytical chemistry, as a precursor to other mercury compounds, as an agent for making amalgams such as aluminium amalgam, and as a catalyst for converting acetylene to vinyl chloride.
How stable is HgCl2 and can it be synthesized?
HgCl2 is thermodynamically stable with respect to its elements and to other mercury–chlorine phases. It can be made by reacting chlorine with metallic mercury or with mercury(I) chloride. Another route is adding hydrochloric acid to a hot, concentrated solution of a mercury(I) compound such as mercury(I) nitrate. It keeps under ordinary storage conditions, although sunlight decomposes it. The solid melts at a fairly low temperature and sublimes unchanged, which is where the name 'sublimate' comes from.
Is HgCl2 a conductor, semiconductor, or insulator?
HgCl2 is an electrical insulator with a wide band gap, consistent with its colourless crystals. Its electronic states are largely tied to the individual Cl–Hg–Cl molecules, and the solid conducts electricity very poorly.
How does HgCl2 compare to other materials in its class?
Among binary metal halides, HgCl2 stands out because its solid is made of molecules. By contrast, alkali halides such as sodium chloride form three-dimensional ionic lattices. Strongly covalent bonding between the group-12 mercury atom and chlorine stabilises the isolated linear molecular units. HgCl2 should not be confused with mercury(I) chloride (Hg2Cl2, calomel), which contains Hg–Hg bonded dimers.
Key Properties
Cross-validated computational properties for Mercury(II) chloride, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of HgCl2. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for HgCl2, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 2.99 | 0.0000 | -0.831 | — |
| Pnma (No. 62) | orthorhombic | 2.89 | 0.0000 | -2.343 | 5.31 |
| Pnma (No. 62) | orthorhombic | 2.66 | 0.0000 | -0.489 | — |
| — | — | 2.88 | 0.0061 | -0.825 | — |
| — | — | 2.87 | 0.0098 | -0.821 | — |
| — | — | 2.87 | 0.0137 | -0.817 | — |
| — | — | 2.00 | 0.0458 | -0.785 | — |
| — | — | 2.17 | 0.0475 | -0.783 | — |
| — | — | 2.17 | 0.0486 | -0.782 | — |
| — | — | 2.24 | 0.0490 | -0.782 | — |
| — | — | 2.09 | 0.0505 | -0.780 | — |
| — | — | 2.15 | 0.0516 | -0.779 | — |
Applications
Where Mercury(II) chloride is used.
Frequently Asked Questions
Common questions about Mercury(II) chloride, answered from cross-validated data and the published literature.
Is HgCl2 the same as calomel?
No. Calomel is mercury(I) chloride (Hg2Cl2). HgCl2 is mercury(II) chloride, historically called corrosive sublimate.
Is mercury(II) chloride dangerous?
Is HgCl2 soluble in water?
Does HgCl2 exist as discrete molecules in the solid state?
Is HgCl2 thermodynamically stable?
What is HgCl2?
What is HgCl2 used for?
What is the band gap of HgCl2?
Is HgCl2 a metal, semiconductor, or insulator?
What is the crystal structure of HgCl2?
What is the density of HgCl2?
How many polymorphs of HgCl2 are known?
What elements does HgCl2 contain?
Where does the data for HgCl2 come from?
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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