Mercury(II) cyanide, also known as mercuric cyanide, is a compound of mercury. It is an odorless, toxic white powder. It is highly soluble in polar solvents such as water, alcohol, and ammonia; slightly soluble in ether; and insoluble in benzene and other hydrophobic solvents.
mercuric cyanide; cyanomercury; mercury cyanide; mercury dicyanide; hydrargyri cyanidum
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||252.63 g/mol|
|Appearance||colorless crystals or white powder|
|Melting point||320 °C (608 °F; 593 K) (decomposes)|
|9.3 g/100 mL (14 °C) |
53.9 g/100 mL (100 °C)
|Solubility||25 g/100 mL (methanol, 19.5 °C) |
soluble in ethanol, ammonia, glycerin
slightly soluble in ether
insoluble in benzene
Refractive index (nD)
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Molecular and crystal structureEdit
At ambient temperature and ambient pressure, Hg(CN)2 takes the form of tetragonal crystals. These crystals are composed of nearly linear Hg(CN)2 molecules with a C-Hg-C bond angle of 175.0° and an Hg-C-N bond angle of 177.0° (Aylett gives slightly different values of 189° and 175°, respectively). Raman spectra show that the molecules distort at higher pressures. Between 16-20 kbar, the structure undergoes a phase transition as the Hg(II) center changes from 2- to 4-coordinate as the CN groups bind to neighboring Hg centers forming via Hg-N bonds. The coordination geometry thus changes from tetragonal to tetrahedral, forming a cubic crystal structure, analogous to the structure of Cd(CN)2. Due to the ambidentate nature of the CN ligands, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.
Mercuric cyanide can be prepared by mixing yellow mercury oxide with hydrocyanic acid in the following chemical reaction which is generally carried out by passing HCN gas into HgO in water. When soluble Hg(CN)2 is formed, the solution is evaporated to crystallize the product.
- HgO + 2 HCN → Hg(CN)2 + H2O
- K4Fe(CN)6 + 3 HgSO4 → 3 Hg(CN)2 + 2 K2SO4 + FeSO4
- Hg2(NO3)2 + 2 KCN → Hg + Hg(CN)2 + 2 KNO3
- Hg(CN)2 → (CN)2 + Hg
Coordination polymers can be synthesized from Hg(CN)2 building blocks. Large single crystals of [(tmeda)Cu-[Hg(CN)2]2][HgCl4] form upon treating CuCl2, the soft Lewis acid Hg(CN)2, and N,N,N',N'-tetramethylethylenediamine (TMEDA). The migration of two labile chloride ligands from harder Cu(II) to softer Hg(II) drives the formation of the crystal.
The use of mercuric cyanide as an antiseptic was discontinued due to its toxicity. Hg(CN)2 is also used in photography. It is still used in homeopathy under the Latin name Hydrargyrum bicyanatum.
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- Kocovsky, P., G. Wang, and V. Sharma. "Mercury(II) Cyanide." e-EROS Encyclopedia of Reagents for Organic Synthesis. Chichester, UK: John Wiley & Sons, Ltd., 2001. http://www.mrw.interscience.wiley.com/eros/articles/rm034/sect0-fs.html
- Wong, P.T.T. J. Chem. Phys. 1984, 80(12), 5937-41.
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- Draper, Neil D.; Batchelor, Raymond J.; Sih, Bryan C.; Ye, Zuo-Guang; Leznoff, Daniel B. (2003). "Synthesis, Structure, and Properties of [(tmeda)Cu[Hg(CN)2]2][HgCl4]: A Non-Centrosymmetric 2-D Layered System that Shows Strong Optical Anisotropy". Chemistry of Materials. 15 (8): 1612–1616. doi:10.1021/cm021716r.
- Benaissa, M.L.; Hantson, P.; Bismuth, C.; Baud, F.J. Intensive Care Med. 1995, 21(12), 1051-1053.
- "Cyanides, Cyanide Oxides and Complex Cyanides." http://www.dncustoms.gov.vn/web_eglish/bieu_thue/E_HTM/E2837.HTM (accessed April 30, 2009).
- Pubchem. "Mercuric cyanide". pubchem.ncbi.nlm.nih.gov. Retrieved 2018-03-22.
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