View source for Cyanate

{{Short description|Anion with formula OCN and charge –1}}
{{Distinguish|fulminate}}

[[File:Cyanate-ion-3D-vdW.png|thumb|right|200px|[[Space-filling model]] of the cyanate anion]]

The '''cyanate ion''' is an [[anion]] with the [[chemical formula]] {{chem2|OCN-}}. It is a [[resonance (chemistry)|resonance]] of three forms: {{chem2|[O-\sC\tN]}} (61%) ↔ {{chem2|[O\dC\dN-]}} (30%) ↔ {{chem2|[O+\tC\sN(2-)]}} (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, {{chem2|CNO-}} or {{chem2|[C-\tN+\sO-]}}.<ref name=mart2019>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. {{doi|10.1080/07370652.2018.1531089}}</ref>

The cyanate ion is an [[ambidentate ligand]], forming [[coordination complex|complexes]] with a metal ion in which either the nitrogen or oxygen atom may be the [[electron donor|electron-pair donor]]. It can also act as a [[bridging ligand]].

Compounds that contain the '''cyanate [[functional group]]''', −O−C≡N, are known as cyanates or [[cyanate ester]]s. The cyanate functional group is distinct from the [[isocyanate]] functional group, −N=C=O; the [[fulminate]] functional group, {{chem2|\sO\sN+\tC-}}; and the [[nitrile oxide]] functional group, {{chem2|\sCNO}} or {{chem2|\sC\tN+\sO-}}.

==Cyanate ion==
The three atoms in a cyanate ion lie on a straight line, giving the ion a linear structure. The [[electronic structure]] is described most simply as
: :Ö̤−C≡N:
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:) The [[infrared spectrum]] of a cyanate salt has a band at ca. 2096&nbsp;cm<sup>−1</sup>; such a high frequency is characteristic of a [[triple bond]].<ref>Nakamoto, Part A, p171</ref>

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]].

==Cyanate salts==
[[Sodium cyanate]] is [[isostructural]] with sodium [[fulminate]], confirming the linear structure of the cyanate ion.<ref>Wells, p722.</ref> It is made industrially by heating a mixture of [[sodium carbonate]] and [[urea]].<ref>Greenwood, p324</ref>
:{{chem2|Na2CO3 + 2 OC(NH2)2 -> 2 NaNCO + CO2 + 2 NH3 + H2O}}
A similar reaction is used to make [[potassium cyanate]]. Cyanates are produced when [[cyanide]]s are oxidized. Use of this fact is made in cyanide decontamination processes where oxidants such as [[permanganate]] and [[hydrogen peroxide]] are used to convert toxic cyanide into less-toxic cyanate.

{|class="wikitable"
!Name
!formula
!Crystal system
!Space group
!Unit cell (Å)
!volume (Å<sup>3</sup>)
!Density (g/cm<sup>3</sup>)
!Comment
!Reference
|-
|[[Ammonium cyanate]]
|NH<sub>4</sub>OCN
|tetragonal
|P4/nmm
|''a''=5.082 ''b''=5.082 ''c''=5.551
|
|
|decomposes when heated to [[urea]]
|<ref>{{cite journal|title=Ammonium cyanate shows N-H···N hydrogen bonding, not N-H···O|author1=MacLean, Elizabeth J. |author2=Harris, Kenneth D. M. |author3=Kariuki, Benson M. |author4=Kitchin, Simon J. |author5=Tykwinski, Rik R. |author6=Swainson, Ian P. |author7=[[Jack Dunitz|Dunitz]] |author8=Jack D.|journal= Journal of the American Chemical Society|year=2003|volume=125|pages=14449–14451|doi=10.1021/ja021156x|pmid=14624593 }}</ref>
|-
|[[Lithium cyanate]]
|LiOCN
|trigonal
|''R''{{overline|3}}''m''
|''a'' = 3.230 ''b'' = 14.268 Z=3
|128.90
|1.895
|melts at 475&nbsp;°C
|<ref>{{cite journal |author1=Erik Hennings |author2=Horst Schmidt |author3=Wolfgang Voigt |title=Structure and Thermal Properties of Lithium Cyanate |journal=Zeitschrift für anorganische und allgemeine Chemie |date=2011 |volume=637 |issue=9 |pages=1199–1202 |doi=10.1002/zaac.201100081 |language=en}}</ref>
|-
|[[Sodium cyanate]]
|NaOCN
|hexagonal
|''R''{{overline|3}}''m''
|''a'' = 3.568 ''c'' = 15.123 
|166.72
|1.94
|melts at 550&nbsp;°C
|<ref>{{cite journal |author1=Olaf Reckeweg |author2=Armin Schulz |author3=Brian Leonard |author4=Francis J. DiSalvo |title=Single-Crystal X-Ray Diffraction Study of Na[OCN] at 170 K and its Vibrational Spectra |journal=Zeitschrift für Naturforschung B |date=2010 |volume=65 |issue=4 |pages=528–532 |doi=10.1515/znb-2010-0416 |language=en|doi-access=free }}</ref>
|-
|[[Potassium cyanate]]
|KOCN
|tetragonal
|''I''4/''mcm''
|''a'' = 6.091 ''c'' = 7.052
|261.6
|2.056
|melts at 315&nbsp;°C
|<ref>{{cite journal |author1=Hiroki Nambu |author2=Mizuhiko Ichikawa |author3=Torbjörn Gustafsson |author4=Ivar Olovsson |title=X-ray diffraction study of KOCN at room temperature |journal=Journal of Physics and Chemistry of Solids |date=2003 |volume=64 |issue=11 |pages=2269–2272 |doi=10.1016/S0022-3697(03)00258-0 |language=en}}</ref>
|-
|[[Rubidium cyanate]]
|RbOCN
|tetragonal
|''I''4/''mcm''
|''a'' = 6.35 ''c'' = 7.38
|297.58
|2.85
|
|<ref name=inorg>T. C. Waddington "Lattice parameters and infrared spectra of some inorganic cyanates" J. Chem. Soc., 1959, 2499-2502. {{doi|10.1039/JR9590002499}}</ref>
|-
|[[Cesium cyanate]]
|CsOCN
|tetragonal
|''I''4''mcm''
|''a'' = 6.519 ''c'' = 7.994
|339.68
|3.42
|
|<ref>{{cite journal |author1=Olaf Reckeweg |author2=Armin Schulz |author3=Francis J. DiSalvo |title=Structural characterization and Raman spectrum of Cs[OCN] |journal=Zeitschrift für Naturforschung B |date=2020 |volume=75 |issue=1–2 |pages=129–133 |doi=10.1515/znb-2019-0168 |language=en|doi-access=free }}</ref>
|-
|[[Thallium cyanate]]
|TlOCN
|tetragonal
|''I''4''mcm''
|''a'' = 6.23 ''c'' = 7.32
|284.3
|5.76
|
|<ref name="inorg" />
|-
|[[Silver cyanate]]
|AgOCN
|monoclinic
|''P''2<sub>1</sub>/''m''
|''a'' = 5.474 ''b'' = 6.378 ''c'' = 3.417 ''β'' = 90.931°
|119.29
|4.173
|melts at 652&nbsp;°C
|<ref>{{cite journal |author1=D.J. Williams |author2=S.C. Vogel |author3=L.L. Daemen |title=Neutron diffraction study of cyanate ligand order/disorder in AgNCO at 300–50K |journal=Physica B: Condensed Matter |date=2006 |volume=385-386 |issue=1 |pages=228–230 |doi=10.1016/j.physb.2006.05.197 |language=en}}</ref>
|-
|[[Strontium cyanate]]
|Sr(OCN)<sub>2</sub>
|orthorhombic
|''Fddd''
|''a'' = 6.151 ''b'' = 11.268 ''c'' = 11.848 Z = 8
|821.1
|2.78
|
|<ref name="Sreu">{{cite journal |author1=Sandro Pagano |author2=Giuseppe Montana |author3=Claudia Wickleder |author4=Wolfgang Schnick |title=Urea Route to Homoleptic Cyanates—Characterization and Luminescence Properties of [M(OCN)2(urea)] and M(OCN)2 with M=Sr, Eu |journal=Chemistry: A European Journal |date=2009 |volume=15 |issue=25 |pages=6186–6193 |doi=10.1002/chem.200900053 |language=en|doi-access=free |pmid=19444832 }}</ref>
|-
|}

==Complexes with the cyanate ion==
Cyanate is an [[ambidentate 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. In ''N''-bonded cyanate complexes the M−NCO unit sometimes has a linear structure, but with ''O''-bonded cyanate the M−O−C unit is bent. Thus, the silver cyanato complex, {{chem2|[Ag(NCO)2]−}}, has a linear structure as shown by [[X-ray crystallography]].<ref name=ChemicalElements>{{Greenwood&Earnshaw2nd|page=325}} (click [https://books.google.com/books?id=EvTI-ouH3SsC&q=cyanato here])</ref> However, the crystal structure of [[silver cyanate]] shows zigzag chains of nitrogen atoms and silver atoms.<ref>{{cite journal |url=https://scripts.iucr.org/cgi-bin/paper?a04540 |first1=D. |last1=Britton |first2=J. D. |last2=Dunitz |title=The crystal structure of silver cyanate |journal=Acta Crystallographica |date=1965 |volume=18 |issue=3 |pages=424–428 |doi=10.1107/S0365110X65000944 |doi-access=free}}</ref> There also exists a structure
    NCO
   /   \
 Ni    Ni
   \   /
    OCN
in which the Ni-N-C group is bent.<ref name=ChemicalElements/>

[[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 {{chem2|[M(OCN)6]^{''n''−}|}}, M&nbsp;= Mo(III), Re(IV), and Re(V). The yellow complex {{chem2|Rh([[triphenylphosphine|PPh3]])3(NCO)}} and orange complex {{chem2|Rh([[triphenylphosphine|PPh3]])3(OCN)}} are [[linkage isomerism|linkage isomers]] and show differences in their infrared spectra which can be used for diagnosis.<ref name=cno>Nakamoto, Part B, pp 121–123.</ref>

The cyanate ion can bridge between two metal atoms by using both its donor atoms. For example, this structure is found in the compound {{chem2|[Ni2(NCO)2([[ethylene diamine|En]])2]([[tetraphenylborate|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.<ref>Greenwood, Table 8.9</ref>

==Cyanate functional group==
Compounds that contain the cyanate [[functional group]], −O−C≡N, are known as cyanates or [[cyanate ester]]s. [[Aryl]] cyanates such are phenyl cyanate, {{chem2|C6H5OCN}} can be formed by a reaction of [[phenol]] with [[cyanogen chloride]], ClCN, in the presence of a base.

[[Organic compound]]s that contain the isocyanate [[functional group]] −N=C=O are known as [[isocyanate]]s. 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]]<ref name=Seymour>{{cite journal |last1=Seymour |first1=Raymond B. |author-link2=George B. Kauffman |last2=Kauffman |first2=George B. |year=1992 |title=Polyurethanes: A Class of Modern Versatile Materials |journal=[[J. Chem. Educ.]] |volume=69 |issue=11 |page=909 |doi=10.1021/ed069p909 |bibcode=1992JChEd..69..909S}}</ref> products and [[pesticide]]s; [[methyl isocyanate]], used to make pesticides, was a major factor in the [[Bhopal disaster]].

==See also==
* [[Cyanide]], {{chem2|CN-}} and [[nitrile]] group, −C≡N
* [[Isocyanide]] or isonitrile group, −N≡C
* [[Thiocyanate]], {{chem2|SCN-}}, −S−C≡N
* [[Selenocyanate]], {{chem2|SeCN-}}, −Se−C≡N
* [[Tellurocyanate]], {{chem2|TeCN-}}, −Te−C≡N
* [[Isocyanate]] group, −N=C=O
* [[Isothiocyanate]] group, −N=C=S
* [[Isoselenocyanate]] group, −N=C=Se

==References==
{{Reflist}}

==External links==
* [https://www.fishersci.com/store/msds?partNumber=AC201111000&countryCode=US&language=en Material Safety Data Sheet for potassium cyanate]

==Bibliography==
*{{Greenwood&Earnshaw2nd}}
*{{cite book|last=Nakamoto|first=K.|title=Infrared and Raman spectra of Inorganic and Coordination compounds|edition=5th|series=Part A|year=1997|publisher=Wiley|isbn=0-471-16394-5}}
*{{cite book|last=Nakamoto|first=K.|title=Infrared and Raman spectra of Inorganic and Coordination compounds|edition=5th|series=Part B|year=1997|publisher=Wiley|isbn=0-471-16392-9}}
*{{cite book|last=Wells|first=A.F|title=Structural Inorganic Chemistry|edition=3rd.|year=1962|publisher=Clarendon Press|location=Oxford|isbn=0-19-855125-8}}

{{Cyanates}}
{{Inorganic compounds of carbon}}
{{Nitrogen compounds}}
{{Functional groups}}

[[Category:Cyanates| ]]
[[Category:Functional groups]]
[[Category:Carbon oxyanions]]
[[Category:Nitrogen oxyanions]]