Silver cyanide is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula AgCN. It is a white solid that precipitated upon treatment of solutions containing Ag⁺ with

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

, which is used in some schemes to recover silver from solution. Silver cyanide is used in silver-plating.

Structure

The structure of silver cyanide consists of - g-CN chains in which the linear two-coordinate Ag⁺ ions are bridged by the cyanide ions, typical of silver(I) and other d¹⁰ ions. This is the same binding mode as seen in the more famous case of

Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyani ...

. These chains then pack hexagonally with adjacent chains offset by +/- 1/3 of the ''c'' lattice parameter. This is the same as the structure adopted by the high temperature polymorph of

copper(I) cyanide 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 ...

. The silver to carbon and silver to nitrogen bond lengths in AgCN are both ~2.09 Å and the cyanide groups show head-to-tail disorder.

Reactions

AgCN precipitates upon the addition of

sodium cyanide Sodium cyanide is a poisonous compound with the formula Na C N. 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 hi ...

to a solution containing Ag⁺. On the addition of further cyanide, the precipitate dissolves to form linear g(CN)₂sup>−_(aq) and g(CN)₃sup>2−_(aq). Silver cyanide is also soluble in solutions containing other ligands such as ammonia or tertiary

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

s. Silver cyanides form structurally complex materials upon reaction with other anions. Some silver cyanides are

luminescent Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal ...

Uses

"Cyanidation" is widely used in the isolation of silver from its ores. Partial purification of silver compounds is usually effected by

froth flotation Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, wher ...

. The silver ion is then separated from the skimmed froth with cyanide, yielding a solution of g(CN)₂sup>−. The silver metal can then be plated out by electrolysis of such solutions. Both AgCN and KAg(CN)₂ have been used in silver-plating solutions since at least 1840 when the Elkington brothers patented their recipe for a silver-plating solution. A typical, traditional silver-plating solution would contain 15-40 g·L⁻¹ KAg(CN)₂ , 12-120 g·L⁻¹ KCN and 15 g·L⁻¹ K₂CO₃.

References

{{Silver compounds Cyanides Silver compounds

Structure

Reactions

Uses

See also

References