Silver cyanide

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Silver cyanide
Identifiers
CAS number 506-64-9 N
ChemSpider 10043 YesY
RTECS number VW3850000
Jmol-3D images Image 1
Properties
Molecular formula AgCN
Molar mass 133.8856 g/mol
Appearance colorless, gray (impure) crystals
Odor odorless
Density 3.943 g/cm3
Melting point 335 °C (635 °F; 608 K) (decomposes)
Solubility in water 0.000023 g/100 mL (20 °C)
Solubility soluble in concentrated ammonia, boiling nitric acid, ammonium hydroxide, KCN
insoluble in alcohol, dilute acid
Refractive index (nD) 1/685
Structure
Crystal structure hexagonal
Coordination
geometry
linear
Thermochemistry
Std molar
entropy
So298
84 J·mol−1·K−1[1]
Std enthalpy of
formation
ΔfHo298
146 kJ·mol−1[1]
Hazards
R-phrases 25-32-33-41-50/53
S-phrases 7-26-45-60-61
Main hazards toxic
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 320 °C (608 °F; 593 K)
LD50 123 mg/kg (oral, rat)
Related compounds
Other anions AgCl
Other cations NaCN
Copper(I) cyanide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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[edit]

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 Å[2] and the cyanide groups show head-to-tail disorder.[3]

Reactions[edit]

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 containing other ligands such as ammonia or tertiary phosphines.

Silver cyanides form structurally complex materials upon reaction with other anions.[4] Some silver cyanides are luminescent.[5]

Uses[edit]

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.[6]


See also[edit]

References[edit]

  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X. 
  2. ^ Hibble, S. J.; Cheyne, S. M.; Hannon, A. C.; Eversfield, S. G.“Beyond Bragg scattering: the structure of AgCN determined from total neutron diffraction” Inorganic Chemistry 2002, volume 41, pages 1042.
  3. ^ Bryce, D. L.; Wasylishen, R.E.“Insight into the Structure of Silver Cyanide from 13C and 15N Solid-State NMR Spectroscopy” Inorganic Chemistry 2002, volume 41, pages 4131.
  4. ^ Urban, V.; Pretsch, T.; Hartl, H. “From AgCN Chains to a Fivefold Helix and a Fishnet-Shaped Framework Structure” Angewandte Chemie International Edition 2005, volume 44, pages 2794–2797.
  5. ^ Omary, M. A.; Webb, T.R.; Assefa, Z.; Shankle, G. E.; Patterson, H. H. “Crystal Structure, Electronic Structure, and Temperature-Dependent Raman Spectra of Tl[Ag(CN)2]: Evidence for Ligand-Unsupported Argentophilic Interactions” Inorganic Chemistry 1998, volume 37, pages 1380-1386.
  6. ^ Blair, A. “Silver Plating” Metal Finishing 2000, volume 98, page 298.