Thecyanate ion is ananion with thechemical formulaOCN−. It is aresonance of three forms:[O−−C≡N] (61%) ↔[O=C=N−] (30%) ↔[O+≡C−N2−] (4%).
Cyanate is the derived anion ofisocyanic acid, H−N=C=O, and its lessertautomer cyanic acid (a.k.a. cyanol), H−O−C≡N.
Any salt containing the ion, such asammonium cyanate, is called a cyanate.
The cyanate ion is anisomer of the much-less-stablefulminate anion,CNO− or[C−≡N+−O−].[1]
The cyanate ion is anambidentate ligand, formingcomplexes with a metal ion in which either the nitrogen or oxygen atom may be theelectron-pair donor. It can also act as abridging ligand.
Compounds that contain thecyanatefunctional group, −O−C≡N, are known as cyanates orcyanate esters. The cyanate functional group is distinct from theisocyanate functional group, −N=C=O; thefulminate functional group,−O−N+≡C−; and thenitrile oxide functional group,−CNO or−C≡N+−O−.
The three atoms in a cyanate ion lie on a straight line, giving the ion a linear structure. Theelectronic structure is described most simply as
with a single C−O bond and a triple C≡N bond. (Or more completely as :Ö̤−C≡N: ↔ Ö̤=C=N̤̈ ↔ :O≡C−N̤̈:) Theinfrared spectrum of a cyanate salt has a band at ca. 2096 cm−1; such a high frequency is characteristic of atriple bond.[2]
The cyanate ion is aLewis base. Both the oxygen and nitrogen atoms carry alone pair of electrons and either one, the other, or both can be donated toLewis acid acceptors. It can be described as anambidentate ligand.
Sodium cyanate isisostructural with sodiumfulminate, confirming the linear structure of the cyanate ion.[3] It is made industrially by heating a mixture ofsodium carbonate andurea.[4]
A similar reaction is used to makepotassium cyanate. Cyanates are produced whencyanides are oxidized. Use of this fact is made in cyanide decontamination processes where oxidants such aspermanganate andhydrogen peroxide are used to convert toxic cyanide into less-toxic cyanate.
| Name | formula | Crystal system | Space group | Unit cell (Å) | volume (Å3) | Density (g/cm3) | Comment | Reference |
|---|---|---|---|---|---|---|---|---|
| Ammonium cyanate | NH4OCN | tetragonal | P4/nmm | a=5.082b=5.082c=5.551 | decomposes when heated tourea | [5] | ||
| Lithium cyanate | LiOCN | trigonal | R3m | a = 3.230b = 14.268 Z=3 | 128.90 | 1.895 | melts at 475 °C | [6] |
| Sodium cyanate | NaOCN | hexagonal | R3m | a = 3.568c = 15.123 | 166.72 | 1.94 | melts at 550 °C | [7] |
| Potassium cyanate | KOCN | tetragonal | I4/mcm | a = 6.091c = 7.052 | 261.6 | 2.056 | melts at 315 °C | [8] |
| Rubidium cyanate | RbOCN | tetragonal | I4/mcm | a = 6.35c = 7.38 | 297.58 | 2.85 | [9] | |
| Cesium cyanate | CsOCN | tetragonal | I4mcm | a = 6.519c = 7.994 | 339.68 | 3.42 | [10] | |
| Thallium cyanate | TlOCN | tetragonal | I4mcm | a = 6.23c = 7.32 | 284.3 | 5.76 | [9] | |
| Silver cyanate | AgOCN | monoclinic | P21/m | a = 5.474b = 6.378c = 3.417β = 90.931° | 119.29 | 4.173 | melts at 652 °C | [11] |
| Strontium cyanate | Sr(OCN)2 | orthorhombic | Fddd | a = 6.151b = 11.268c = 11.848 Z = 8 | 821.1 | 2.78 | [12] |
Cyanate is anambidentate ligand which can donate the pair of electrons on the nitrogen atom or the oxygen atom, or both. Structurally the isomers can be distinguished by the geometry of the complex. InN-bonded cyanate complexes the M−NCO unit sometimes has a linear structure, but withO-bonded cyanate the M−O−C unit is bent. Thus, the silver cyanato complex,[Ag(NCO)2]−, has a linear structure as shown byX-ray crystallography.[13] However, the crystal structure ofsilver cyanate shows zigzag chains of nitrogen atoms and silver atoms.[14] There also exists a structure
NCO / \Ni Ni \ / OCN
in which the Ni-N-C group is bent.[13]
Infrared spectroscopy has been used extensively to distinguish between isomers. Many complexes ofdivalent metals areN-bonded.O-Bonding has been suggested for complexes of the type[M(OCN)6]n−, M = Mo(III), Re(IV), and Re(V). The yellow complexRh(PPh3)3(NCO) and orange complexRh(PPh3)3(OCN) arelinkage isomers and show differences in their infrared spectra which can be used for diagnosis.[15]
The cyanate ion can bridge between two metal atoms by using both its donor atoms. For example, this structure is found in the compound[Ni2(NCO)2(En)2](BPh4)2. 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.[16]
Compounds that contain the cyanatefunctional group, −O−C≡N, are known as cyanates orcyanate esters.Aryl cyanates such are phenyl cyanate,C6H5OCN can be formed by a reaction ofphenol withcyanogen chloride, ClCN, in the presence of a base.
Organic compounds that contain the isocyanatefunctional group −N=C=O are known asisocyanates. It is conventional inorganic chemistry to write isocyanates with two double bonds, which accords with a simplisticvalence bond theory of the bonding. Innucleophilic substitution reactions cyanate usually forms an isocyanate. Isocyanates are widely used in the manufacture ofpolyurethane[17] products andpesticides;methyl isocyanate, used to make pesticides, was a major factor in theBhopal disaster.
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