Silver cyanide


Silver cyanide is the chemical compound with the formula AgCN. This white solid forms upon treatment of solutions containing Ag+ with cyanide. This precipitation step is used in some schemes to recover silver from solution. Silver cyanide is used in silver-plating.

Structure

Its structure consist of -- chains in which the linear two-coordinate Ag+ ions, typical of silver and other d10 ions are bridge by the cyanide ions. These chains then pack hexagonally with adjacent chains ofset by +/- 1/3 of the "c" lattice parameter. This is the same as the structure adopted by the high temperature polymorph of copper cyanide. 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 to a solution containing Ag+. The precipitate dissolves upon the addition of further amounts of cyanide to form linear − and 2− on the addition of further cyanide. Silver cyanide is also soluble in solutions containing other ligands such as ammonia or tertiary phosphines.
Silver cyanides form structurally complex materials upon reaction with other anions. Some silver cyanides are luminescent.

Uses

Both AgCN and KAg2 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 KAg2 15-40 gL−1, KCN 12-120 gL−1 and K2CO3 gL−1.