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==Examples of pseudohalogen molecules==
==Examples of pseudohalogen molecules==
Examples of symmetrical pseudohalogens ({{chem2|Ps\sPs}}) include [[cyanogen]] (CN)<sub>2</sub>, [[thiocyanogen]] (SCN)<sub>2</sub>, [[hydrogen peroxide]] H<sub>2</sub>O<sub>2</sub>. Another complex symmetrical pseudohalogen is [[dicobalt octacarbonyl]], Co<sub>2</sub>(CO)<sub>8</sub>. This substance can be considered as a [[Dimer (chemistry)|dimer]] of the [[hypothetical]] cobalt tetracarbonyl, Co(CO)<sub>4</sub>.
Examples of symmetrical pseudohalogens {{chem2|Ps\sPs}}, where Ps is an abbreviation of a pseudohalogen, include [[cyanogen]] (CN)<sub>2</sub>, [[thiocyanogen]] (SCN)<sub>2</sub>, [[hydrogen peroxide]] H<sub>2</sub>O<sub>2</sub>. Another complex symmetrical pseudohalogen is [[dicobalt octacarbonyl]], Co<sub>2</sub>(CO)<sub>8</sub>. This substance can be considered as a [[Dimer (chemistry)|dimer]] of the [[hypothetical]] cobalt tetracarbonyl, Co(CO)<sub>4</sub>.


Examples of non-symmetrical pseudohalogens (''Ps''–X), analogous to the binary [[Interhalogen|interhalogen compound]]s, are [[cyanogen halide]]s like [[Cyanogen chloride|ClCN]] or [[Cyanogen bromide|BrCN]]; [[nitryl fluoride]], and other compounds. Sometimes [[nitrosyl chloride]] NOCl also is considered as pseudohalogen.
Examples of non-symmetrical pseudohalogens (''Ps''–X), analogous to the binary [[Interhalogen|interhalogen compound]]s, are [[cyanogen halide]]s like [[Cyanogen chloride|ClCN]] or [[Cyanogen bromide|BrCN]]; [[nitryl fluoride]], and other compounds. Sometimes [[nitrosyl chloride]] NOCl also is considered as pseudohalogen.

Revision as of 19:56, 23 February 2023

Pseudohalogens are polyatomic analogues of halogens, whose chemistry, resembling that of the true halogens, allows them to substitute for halogens in several classes of chemical compounds.[1] Pseudohalogens occur in pseudohalogen molecules, inorganic molecules of the general forms PsPs or Ps–X (where Ps is a pseudohalogen group), such as cyanogen; pseudohalide anions, such as cyanide ion; inorganic acids, such as hydrogen cyanide; as ligands in coordination complexes, such as ferricyanide; and as functional groups in organic molecules, such as the nitrile group. Well-known pseudohalogen functional groups include cyanide, cyanate, thiocyanate, and azide.

Common pseudohalogens and their nomenclature

Many pseudohalogens are known by specialized common names according to where they occur in a compound. Well-known ones include (the true halogen chlorine is listed for comparison):

Group Dimer Hydrogen compound Pseudohalide Ligand name In organic compounds Formula Structural formula
True halogens
chloro chlorine
(dichlorane)
Hydrogen chloride
(chlorane)
chloride chlorido-
chloro-
-yl chloride ~ Cl −Cl
Pseudohalogens
cyano cyanogen hydrogen cyanide,
prussic acid,
formonitrile
cyanide cyanido-
cyano-
-nitrile
-yl cyanide
~ CN −C≡N
cyapho cyaphogen phosphaethyne cyaphide cyaphido-
cyapho-
-yl cyaphide ~ CP −C≡P
isocyano isocyanogen hydrogen isocyanide,
isohydrocyanic acid
isocyanide isocyanido-
isocyano-
-isonitrile
-yl isocyanide
~ NC −N+≡C
hydroxyl hydrogen peroxide
(dioxidane)
water
(oxidane)
hydroxide hydroxido-
hydroxy-
-ol ~ OH −O−H
sulfanyl hydrogen disulfide
(disulfane)
hydrogen sulfide
(sulfane)
hydrosulfide sulfanido-
thiolato-
-thiol
-yl mercaptane
~ SH −S−H
selanyl hydrogen diselenide
(diselane)
hydrogen selenide
(selane)
hydroselenide selanido-
selenolato-
-selenol ~ SeH −Se−H
tellanyl hydrogen ditelluride
(ditellane)
hydrogen telluride
(tellane)
hydrotelluride tellanido-
tellurolato-
-tellurol ~ TeH −Te−H
cyanate dicyanodioxidane cyanic acid cyanate cyanato- -yl cyanate ~ OCN −O−C≡N
isocyanate isocyanogen isocyanic acid isocyanate isocyanato- -yl isocyanate ~ NCO −N=C=O
fulminate fulminogen fulminic acid fulminate fulminato- -nitrile oxide
-yl fulminate
~ CNO −C≡N+−O
thiocyanate,
rhodanide
thiocyanogen thiocyanic acid thiocyanate thiocyanato- -yl thiocyanate ~ SCN −S−C≡N
isothiocyanate isothiocyanogen isothiocyanic acid isothiocyanate isothiocyanato- -yl isothiocyanate ~ NCS −N=C=S
selenocyanate,
selenorhodanide
selenocyanogen selenocyanic acid selenocyanate selenocyanato- -yl selenocyanate ~ SeCN −Se−C≡N
tellurocyanate,[2]
tellurorhodanide
tellurocyanogen tellurocyanic acid tellurocyanate tellurocyanato- -yl tellurocyanate ~ TeCN −Te−C≡N
azide azidogen hydrazoic acid azide azido- -yl azide N3 −N−N+≡N

−N=N+=N
nitric oxide dinitrogen dioxide nitroxyl nitroxide nitrosyl nitroso- ~ NO −N=O
nitrogen dioxide dinitrogen tetroxide nitryl nitro- NO2 −NO2
cobalt carbonyl dicobalt octacarbonyl cobalt tetracarbonyl hydride tetracarbonylcobaltate Co(CO)4 −Co(C≡O)4
trinitromethanide hexanitroethane nitroform,
trinitromethane
trinitromethanide trinitromethanido- -yl trinitromethanide C(NO2)3 −C(−NO2)3
tricyanomethanide hexacyanoethane cyanoform,
tricyanomethane
tricyanomethanide tricyanomethanido- -yl tricyanomethanide C(CN)3 −C(−C≡N)3
1,2,3,4-thiatriazol-5-thiolate bis(1,2,3,4-thiatriazol-5-yl)disulfane 1,2,3,4-thiatriazol-5-thiol[3] 1,2,3,4-thiatriazol-5-thiolate 1,2,3,4-thiatriazol-5-thiolato- -yl 1,2,3,4-thiatriazol-5-thiolate CS2N3[4]

Au is considered to be a pseudohalogen ion due to its disproportionation reaction with alkali and the ability to form covalent bonds with hydrogen.[5]

Examples of pseudohalogen molecules

Examples of symmetrical pseudohalogens Ps−Ps, where Ps is an abbreviation of a pseudohalogen, include cyanogen (CN)2, thiocyanogen (SCN)2, hydrogen peroxide H2O2. Another complex symmetrical pseudohalogen is dicobalt octacarbonyl, Co2(CO)8. This substance can be considered as a dimer of the hypothetical cobalt tetracarbonyl, Co(CO)4.

Examples of non-symmetrical pseudohalogens (Ps–X), analogous to the binary interhalogen compounds, are cyanogen halides like ClCN or BrCN; nitryl fluoride, and other compounds. Sometimes nitrosyl chloride NOCl also is considered as pseudohalogen.

Not all combinations are known to be stable.

Pseudohalides

Pseudohalides are the univalent anions (or functional groups) which form hydracids with hydrogen and form insoluble salts with silver such as cyanide, cyanates, fulminate, thiocyanate and azide.

A common complex pseudohalide is a tetracarbonylcobaltate [Co(CO)
4
]
. The acid HCo(CO)4 is in fact quite a strong acid, though its low solubility renders it not as strong as the true hydrohalic acids.

The behavior and chemical properties of the above pseudohalides are identical to that of the true halide ions. The presence of the internal multiple bonds does not appear to affect their chemical behavior. For example, they can form strong acids of the type HX (compare HCl to HCo(CO)4), and they can react with metals to form compounds like MX (compare NaCl to NaN3).

Nanoclusters of aluminium (often referred to as superatoms) are sometimes considered to be pseudohalides since they, too, behave chemically as halide ions, forming Al13I2 (analogous to I3) and similar compounds. This is due to the effects of metallic bonding on small scales.

References

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "pseudohalogens". doi:10.1351/goldbook.P04930
  2. ^ "Tellurocyanate | CNTe | ChemSpider". Archived from the original on 2021-11-21.
  3. ^ https://pubchem.ncbi.nlm.nih.gov/compound/12821433
  4. ^ Margaret-Jane Crawford, et al. CS2N3, A Novel Pseudohalogen. J. Am. Chem. Soc. 2000, 122, 9052-9053
  5. ^ Mudring, Anjy-Verena; Jansen, Martin (2000-11-28). "ChemInform Abstract: Base-Induced Disproportionation of Elemental Gold". ChemInform. 31 (48): no. doi:10.1002/chin.200048020.