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The cyanate ion is an anion with the chemical formula . It is a resonance of three forms: (61%) ↔ (30%) ↔ (4%).
Cyanate is the derived anion of isocyanic acid, H−N=C=O, and its lesser tautomer cyanic acid (a.k.a. cyanol), H−O−C≡N.
Any salt containing the ion, such as ammonium cyanate, is called a cyanate.
The cyanate ion is an isomer of the much-less-stable fulminate anion, or .William R. Martin and David W. Ball (2019): "Small organic fulminates as high-energy materials. Fulminates of acetylene, ethylene, and allene". Journal of Energetic Materials, volume 31, issue 7, pages 70-79.
The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron donor. It can also act as a bridging ligand.
Compounds that contain the cyanate functional group, −O−C≡N, are known as cyanates or . The cyanate functional group is distinct from the isocyanate functional group, −N=C=O; the fulminate functional group, ; and the nitrile oxide functional group, or .
The cyanate ion is a Lewis base. Both the oxygen and nitrogen atoms carry a lone pair of electrons and either one, the other, or both can be donated to Lewis acid acceptors. It can be described as an ambidentate ligand.
| Ammonium cyanate | NH4OCN | tetragonal | P4/nmm | a=5.082 b=5.082 c=5.551 | decomposes when heated to urea | |||
| Lithium cyanate | LiOCN | trigonal | R m | a = 3.230 b = 14.268 Z=3 | 128.90 | 1.895 | melts at 475 °C | |
| Sodium cyanate | NaOCN | hexagonal | R m | a = 3.568 c = 15.123 | 166.72 | 1.94 | melts at 550 °C | |
| Potassium cyanate | KOCN | tetragonal | I4/ mcm | a = 6.091 c = 7.052 | 261.6 | 2.056 | melts at 315 °C | |
| Rubidium cyanate | RbOCN | tetragonal | I4/ mcm | a = 6.35 c = 7.38 | 297.58 | 2.85 | T. C. Waddington "Lattice parameters and infrared spectra of some inorganic cyanates" J. Chem. Soc., 1959, 2499-2502. | |
| Cesium cyanate | CsOCN | tetragonal | I4 mcm | a = 6.519 c = 7.994 | 339.68 | 3.42 | ||
| Thallium cyanate | TlOCN | tetragonal | I4 mcm | a = 6.23 c = 7.32 | 284.3 | 5.76 | ||
| Silver cyanate | AgOCN | monoclinic | P21/ m | a = 5.474 b = 6.378 c = 3.417 β = 90.931° | 119.29 | 4.173 | melts at 652 °C | |
| Strontium cyanate | Sr(OCN)2 | orthorhombic | Fddd | a = 6.151 b = 11.268 c = 11.848 Z = 8 | 821.1 | 2.78 | ||
NCO
/ \
Ni Ni
\ /
OCN
in which the Ni-N-C group is bent.
Infrared spectroscopy has been used extensively to distinguish between isomers. Many complexes of divalent metals are N-bonded. O-Bonding has been suggested for complexes of the type , M = Mo(III), Re(IV), and Re(V). The yellow complex and orange complex are linkage isomers and show differences in their infrared spectra which can be used for diagnosis.Nakamoto, Part B, pp 121–123.
The cyanate ion can bridge between two metal atoms by using both its donor atoms. For example, this structure is found in the compound . In this compound both the Ni−N−C unit and Ni−O−C unit are bent, even though in the first case donation is through the nitrogen atom.Greenwood, Table 8.9
that contain the isocyanate functional group −N=C=O are known as . It is conventional in organic chemistry to write isocyanates with two double bonds, which accords with a simplistic valence bond theory of the bonding. In nucleophilic substitution reactions cyanate usually forms an isocyanate. Isocyanates are widely used in the manufacture of polyurethane products and ; methyl isocyanate, used to make pesticides, was a major factor in the Bhopal disaster.
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