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 -[Ag-CN]- chains in which the linear two-coordinate Ag+ ions, typical of silver(I) and other d10 ions are bridge by the cyanide ions. (This is the same binding mode as seen in the more famous case of [|Prussian blue].) 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(I) cyanide]. The silver to carbon and silver to nitrogen bond lengths in AgCN are both ~2.09 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 [Ag(CN)2]-(aq) and [Ag(CN)3]2-(aq) on the addition of further cyanide. Silver cyanide is also soluble in solutions containg 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 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 KAg(CN)2 15-40 gL−1, KCN 12-120 gL−1 and K2CO3 gL−1.