Mercury(II) cyanide

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Mercury(II) cyanide
Mercury(II)-cyanide-3D-vdW.png
Mercuric cyanide.png
Names
IUPAC name
dicyanomercury
Other names
mercuric cyanide; cyanomercury; neutral mercury cyanide (1:2); mercury dicyanide; hydrargyri cyanidum [1] (homeopathy)
Identifiers
3D model (JSmol)
3679510
ChEBI
ChemSpider
ECHA InfoCard 100.008.857 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 209-741-6
2563
PubChem CID
UNII
UN number 1636
  • InChI=1S/2CN.Hg/c2*1-2;
    Key: FQGYCXFLEQVDJQ-UHFFFAOYSA-N
  • InChI=1/2CN.Hg/c2*1-2;/rC2HgN2/c4-1-3-2-5
    Key: FQGYCXFLEQVDJQ-RYFBSBGDAX
  • C(#N)[Hg]C#N
Properties
Hg(CN)2
Molar mass 252.63 g/mol
Appearancecolorless crystals or white powder
Odor odorless
Density 3.996 g/cm3
Melting point 320 °C (608 °F; 593 K) [2] (decomposes)
9.3 g/100 mL (14 °C)
53.9 g/100 mL (100 °C) [3]
Solubility 25 g/100 mL (methanol, 19.5 °C)
soluble in ethanol, ammonia, glycerin
slightly soluble in ether
insoluble in benzene
67.0·10−6 cm3/mol
1.645
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Highly toxic
GHS labelling: [4]
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H300, H301, H310, H330, H373, H410
P260, P262, P264, P270, P271, P273, P280, P284, P301+P310, P302+P350, P304+P340, P310, P314, P320, P322, P330, P361, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard POI: Poisonous
4
0
2
POI
Lethal dose or concentration (LD, LC):
26 mg/kg
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Mercury(II) cyanide, also known as mercuric cyanide, is a poisonous compound of mercury and cyanide. 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. [2]

Contents

Molecular and crystal structure

At ambient temperature and ambient pressure, Hg(CN)2 takes the form of tetragonal crystals. [2] 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 [3] 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. [6]

As in the solid state, in aqueous solution, Hg(CN)2 molecules are linear. [3]

Synthesis

Mercuric cyanide can be prepared by mixing yellow mercury oxide with hydrocyanic acid in the following chemical reaction [3] 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. [1]

HgO + 2 HCN → Hg(CN)2 + H2O

Hg(CN)2 can also be prepared by mixing HgO with finely powdered Prussian blue. [3] [7] In addition, it can be produced by reacting mercuric sulfate with potassium ferrocyanide in water: [7]

K4Fe(CN)6 + 3 HgSO4 → 3 Hg(CN)2 + 2 K2SO4 + FeSO4

Another method to generate mercuric cyanide is through the disproportionation of mercury(I) derivatives. In these reactions, metallic mercury precipitates, and Hg(CN)2 remains in solution: [7]

Hg2(NO3)2 + 2 KCN → Hg + Hg(CN)2 + 2 KNO3

Reactions

It rapidly decomposes in acid to give off hydrogen cyanide. It is photosensitive, becoming darker in color. [8]

Mercury cyanide catalyzes the Koenigs–Knorr reaction for the synthesis of glycosides. [2] Cyanogen, (CN)2, forms upon heating dry mercury cyanide, but the method is inferior to other routes: [9]

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. [10]

Past applications

The use of mercuric cyanide as an antiseptic was discontinued due to its toxicity. [11] Hg(CN)2 is also used in photography. [12]

Toxicology

Mercury(II) cyanide is poison with health hazard classification 3, having an oral LD50 of 33 milligrams per kilogram in mice and a subcutaneous LD50 of 2.7 milligrams per kilogram in dogs. [13]

Related Research Articles

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Sodium cyanide is a poisonous compound with the formula NaCN. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its high reactivity toward metals. It is a moderately strong base.

Cyanogen is the chemical compound with the formula (CN)2. The simplest stable carbon nitride, it is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing. The two cyano groups are bonded together at their carbon atoms: N≡C‒C≡N, although other isomers have been detected. The name is also used for the CN radical, and hence is used for compounds such as cyanogen bromide (NCBr) (but see also Cyano radical.)

<span class="mw-page-title-main">Copper(II) sulfate</span> Chemical compound

Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula CuSO4. It forms hydrates CuSO4·nH2O, where n can range from 1 to 7. The pentahydrate (n = 5), a bright blue crystal, is the most commonly encountered hydrate of copper(II) sulfate. Older names for the pentahydrate include blue vitriol, bluestone, vitriol of copper, and Roman vitriol. It exothermically dissolves in water to give the aquo complex [Cu(H2O)6]2+, which has octahedral molecular geometry. The structure of the solid pentahydrate reveals a polymeric structure wherein copper is again octahedral but bound to four water ligands. The Cu(II)(H2O)4 centers are interconnected by sulfate anions to form chains. Anhydrous copper sulfate is a light grey powder.

<span class="mw-page-title-main">Potassium cyanide</span> Highly toxic crystalline salt

Potassium cyanide is a compound with the formula KCN. It is a colorless salt, similar in appearance to sugar, that is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewellery for chemical gilding and buffing. Potassium cyanide is highly toxic, and a dose of 200 to 300 milligrams will kill nearly any human.

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Copper(I) cyanide is an inorganic compound with the formula CuCN. This off-white solid occurs in two polymorphs; impure samples can be green due to the presence of Cu(II) impurities. The compound is useful as a catalyst, in electroplating copper, and as a reagent in the preparation of nitriles.

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References

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  3. 1 2 3 4 5 Aylett, B.J. "Mercury (II) Pseudohalides: Cyanide, Thiocyanate, Selenocyanate, Azide, Fulminate." Comprehensive Inorganic Chemistry 3:304-306. J.C. Bailar, Harry Julius Emeléus, Sir Ronald Nyholm, and A.F. Trotman-Dickenson, ed. Oxford: Pergamon Press, 1973; distributed by Compendium Publishers (Elmsford, NY), p. 304.
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  10. 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.
  11. Benaissa, M.L.; Hantson, P.; Bismuth, C.; Baud, F.J. Intensive Care Med.1995, 21(12), 1051-1053.
  12. "Cyanides, Cyanide Oxides and Complex Cyanides." http://www.dncustoms.gov.vn/web_eglish/bieu_thue/E_HTM/E2837.HTM Archived 2017-12-30 at the Wayback Machine (accessed April 30, 2009).
  13. Pubchem. "Mercuric cyanide". pubchem.ncbi.nlm.nih.gov. Retrieved 2018-03-22.