Silver azide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Silver azide
Silver-azide-high-T-single-layer-3D-vdW.png
Identifiers
CAS number 13863-88-2
PubChem 61698
ChemSpider 55601 YesY
Jmol-3D images Image 1
Properties
Molecular formula AgN3
Molar mass 149.888 g/mol
Appearance colorless solid
Density 4.42 g/cm3, solid
Melting point 250 °C, explosive
Boiling point decomp.
Solubility in other solvents 2.0×10-8 g/L
Structure
Crystal structure Orthorhombic oI16[1]
Space group Ibam, No 72
Hazards
Main hazards Very toxic, explosive
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g., nitroglycerin Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Silver azide is the chemical compound with the formula AgN3. This colorless solid is a well-known explosive.

Structure and chemistry[edit]

Silver azide can be prepared by treating an aqueous solution of silver nitrate with sodium azide.[2] The silver azide precipitates as a white solid, leaving sodium nitrate in solution.

AgNO
3
(aq) + NaN
3
(aq) → AgN
3
(s) + NaNO
3
(aq)

X-ray crystallography shows that AgN3 is a coordination polymer with square planar Ag+ coordinated by four azide ligands. Correspondingly, each end of each azide ligand is connected to a pair of Ag+ centers. The structure consists of two-dimensional AgN3 layers stacked one on top of the other, with weaker Ag–N bonds between layers. The coordination of Ag+ can alternatively be described as highly distorted 4 + 2 octahedral, the two more distant nitrogen atoms being part of the layers above and below.[3]

Silver-azide-high-T-single-layer-3D-balls.png
Silver-azide-high-T-layer-stacking-3D-balls.png
Silver-azide-high-T-Ag-coordination-3D-balls-A.png
Silver-azide-high-T-N-coordination-3D-balls-B.png
Part of a layer
Layer stacking
4 + 2 coordination of Ag+
2 + 1 coordination of N in N
3

In its most characteristic reaction, the solid decomposes explosively, releasing nitrogen gas:

2 AgN
3
(s) → 3 N
2
(g) + 2 Ag (s)

The first step in this decomposition is the production of free electrons and azide radicals; thus the reaction rate is increased by the addition of semiconducting oxides.[4] Pure silver azide explodes at 340 °C, but the presence of impurities lowers this down to 270 °C.[5] This reaction has a lower activation energy and initial delay than the corresponding decomposition of lead azide.[6]

Safety[edit]

AgN3, like most heavy metal azides, is dangerously explosive. Decomposition can be triggered by exposure to ultraviolet light or by impact.[2] Ceric ammonium nitrate is used as an oxidising agent to destroy AgN
3
in spills.[5]

See also[edit]

References[edit]

  1. ^ Marr H.E. III., Stanford R.H. Jr. (1962). "The unit-cell dimensions of silver azide". Acta Crystallographica 15 (12): 1313–1314. doi:10.1107/S0365110X62003497. 
  2. ^ a b Jacqueline Akhavan (2004). The chemistry of explosives (2nd ed.). Royal Society of Chemistry. pp. 30–31. ISBN 0-85404-640-2. 
  3. ^ Schmidt, C. L. Dinnebier, R.; Wedig, U.; Jansen, M. (2007). "Crystal Structure and Chemical Bonding of the High-Temperature Phase of AgN3". Inorganic Chemistry 46 (3): 907–916. doi:10.1021/ic061963n. PMID 17257034. 
  4. ^ Andrew Knox Galwey; Michael E. Brown (1999). Thermal decomposition of ionic solids (vol.86 of Studies in physical and theoretical chemistry. Elsevier. p. 335. ISBN 0-444-82437-5. 
  5. ^ a b Margaret-Ann Armour (2003). Hazardous laboratory chemicals disposal guide, Environmental Chemistry and Toxicology (3rd ed.). CRC Press. p. 452. ISBN 1-56670-567-3. 
  6. ^ Jehuda Yinon; Shmuel Zitrin (1996). Modern Methods and Applications in Analysis of Explosives. John Wiley and Sons. pp. 15–16. ISBN 0-471-96562-6.