Mercury(II) cyanide
Encyclopedia
Mercury cyanide, also known as mercuric cyanide, is a coordination compound of nitrogen
, carbon
and mercury
. It is a colorless, odorless, toxic
white powder with a bitter metallic taste. It has a melting point of 320°C, at which it decomposes and releases toxic mercury fumes. It is highly soluble
in polar
solvent
s such as water
, alcohol
, and ammonia
; slightly soluble in ether
; and insoluble in benzene
and other hydrophobic
solvents. It rapidly decomposes in acid
to give off hydrogen cyanide. Samples also decompose when exposed to light, becoming darker in color. It reacts vigorously with oxidizing agent
s; fusion with metal chlorate
s, perchlorate
s, nitrate
s, or nitrite
s can cause a violent explosion.
and ambient pressure
, Hg(CN)2 takes the form of tetragonal crystals
. These crystals are composed of nearly linear Hg(CN)2 molecule
s 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 ligand
s, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.
As in the solid state, aqueous solution
, Hg(CN)2 molecules are linear.
with hydrocyanic acid in the following chemical reaction
. This reaction 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.
Hg(CN)2 can also be prepared by mixing HgO, finely powdered Prussian blue
In addition, Hg(CN)2 can be produced by reacting mercuric sulfate
with potassium ferrocyanide
in water:
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:
in the Koenigs–Knorr reaction for the synthesis of glycoside
s. Cyanogen
, (CN)2, forms upon heating dry mercury cyanide but the method is inferior to other routes:
Coordination polymers can be synthesized from Hg(CN)2 building blocks. Large single crystals of [(tmeda)Cu-[Hg(CN)2]2][HgCl4] form upon reacting the labile
transition metal
halide 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.
, but this practice has been discontinued due to its toxicity. One example of this was the treatment of syphilis
: a solution of 5-10 grains in an ounce of water, painted on with a camel
-hair brush, was applied to syphilitic sores of the tongue or mouth. Hg(CN)2 is also used in photography
. It is still used in homeopathy
under the Latin name Hydrargyrum bicyanatum.
and its two cyanide groups
.
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. It is a colorless, odorless, toxic
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
white powder with a bitter metallic taste. It has a melting point of 320°C, at which it decomposes and releases toxic mercury fumes. It is highly soluble
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
in polar
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s such as water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
; slightly soluble in ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
; and insoluble in benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
and other hydrophobic
Hydrophobe
In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
solvents. It rapidly decomposes in acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
to give off hydrogen cyanide. Samples also decompose when exposed to light, becoming darker in color. It reacts vigorously with oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
s; fusion with metal chlorate
Chlorate
The chlorate anion has the formula ClO. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a roman numeral in parentheses, e.g...
s, perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...
s, nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s, or nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
s can cause a violent explosion.
Molecular and crystal structure
At ambient temperatureRoom temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
and ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
, Hg(CN)2 takes the form of tetragonal crystals
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
. These crystals are composed of nearly linear Hg(CN)2 molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s with a C-Hg-C bond angle
Molecular geometry
Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...
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
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
show that the molecules distort at higher pressures. Between 16-20 kbar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
, the structure undergoes a phase transition as the Hg(II) center changes from 2- to 4-coordinate
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
as the CN groups bind to neighboring Hg centers forming via Hg-N bonds. The coordination geometry thus changes from tetragonal to tetrahedral
Tetrahedral symmetry
150px|right|thumb|A regular [[tetrahedron]], an example of a solid with full tetrahedral symmetryA regular tetrahedron has 12 rotational symmetries, and a symmetry order of 24 including transformations that combine a reflection and a rotation.The group of all symmetries is isomorphic to the group...
, forming a cubic crystal structure
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
, analogous to the structure of Cd(CN)2. Due to the ambidentate nature of the CN ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.
As in the solid state, aqueous solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
, Hg(CN)2 molecules are linear.
Synthesis
Mercuric cyanide can be prepared by mixing yellow mercury oxideMercury(II) oxide
Mercury oxide, also called mercuric oxide or simply mercury oxide, has a formula of HgO. It has a red or orange color. Mercury oxide is a solid at room temperature and pressure...
with hydrocyanic acid in the following chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
. This reaction 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
Crystallization
Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...
the product.
- HgO + 2 HCN → Hg(CN)2 + H2O
Hg(CN)2 can also be prepared by mixing HgO, finely powdered Prussian blue
Prussian blue
Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....
In addition, Hg(CN)2 can be produced by reacting mercuric sulfate
Mercury(II) sulfate
Mercury sulfate, commonly called mercuric sulfate is the chemical compound Hg S O4. It is an odorless solid that forms white granules or crystalline powder...
with potassium ferrocyanide
Potassium ferrocyanide
Potassium ferrocyanide is the inorganic compound with formula K4[Fe6]•3H2O. It is the potassium salt of the coordination complex [Fe6]4-. This salt forms lemon-yellow monoclinic crystals.-Synthesis:...
in water:
- 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
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
, and Hg(CN)2 remains in solution:
- Hg2(NO3)2 + 2 KCN → Hg + Hg(CN)2 + 2 KNO3
Reactions
Mercury cyanide can be used as a promoterCatalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
in the Koenigs–Knorr reaction for the synthesis of glycoside
Glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme...
s. Cyanogen
Cyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, 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...
, (CN)2, forms upon heating dry mercury cyanide but the method is inferior to other routes:
- 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 reacting the labile
Lability
Lability refers to something that is constantly undergoing change or something that is likely to undergo change.-Chemistry:The term is used to describe a relatively unstable and transient chemical species...
transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
halide CuCl2
Copper(II) chloride
Copper chloride is the chemical compound with the formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate. The copper chlorides are some of the most common copper compounds, after copper sulfate....
, the soft
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
Lewis acid Hg(CN)2, and N,N,N',N'-tetramethylethylenediamine (TMEDA)
Tetramethylethylenediamine
Tetramethylethylenediamine is a chemical compound with the formula 2NCH2CH2N2. This species is derived from ethylenediamine by replacement of the four N-H groups with four N-methyl groups. Its odor is remarkably similar to that of fish.-As a reagent in organic and inorganic synthesis:TMEDA is...
. The migration of two labile chloride ligands from harder
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
Cu(II) to softer
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
Hg(II) drives the formation of the crystal.
Past applications
Mercuric cyanide was once used as an antisepticAntiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
, but this practice has been discontinued due to its toxicity. One example of this was the treatment of syphilis
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...
: a solution of 5-10 grains in an ounce of water, painted on with a camel
Camel
A camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
-hair brush, was applied to syphilitic sores of the tongue or mouth. Hg(CN)2 is also used in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
. It is still used in homeopathy
Homeopathy
Homeopathy is a form of alternative medicine in which practitioners claim to treat patients using highly diluted preparations that are believed to cause healthy people to exhibit symptoms that are similar to those exhibited by the patient...
under the Latin name Hydrargyrum bicyanatum.
Toxicology
Mercury(II) cyanide is one of the most toxic poisons. Its high toxicity is due to mercuryMercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...
and its two cyanide groups
Cyanide poisoning
Cyanide poisoning occurs when a living organism is exposed to a compound that produces cyanide ions when dissolved in water. Common poisonous cyanide compounds include hydrogen cyanide gas and the crystalline solids potassium cyanide and sodium cyanide...
.