Pentacyanocyclopentadiene is a

derivative In mathematics, the derivative is a fundamental tool that quantifies the sensitivity to change of a function's output with respect to its input. The derivative of a function of a single variable at a chosen input value, when it exists, is t ...

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−. This colorless liquid has a strong and unpleasant odor. At room temperature, ...

with five

cyano group In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This an ...

s with the molecular formula C₅H(CN)₅. The corresponding

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

, pentacyanocyclopentadienide, is a

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

with the molecular formula . In contrast to other anions based on a C₅ ring unit it binds to metals through the pendant cyano groups rather than the C₅ ring. The anion was first synthesised by Webster in the 1960s and its conjugate acid much later on. More recently Wright has discovered its extensive coordination chemistry. By virtue of a combination of mesomeric and aromatic stabilization of its anion, pentacyanocyclopentadiene is a

superacid In chemistry, a superacid (according to the original definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid i ...

, with an estimated aqueous p''K''_a of −11. The free acid was prepared by Reed in 2004 and was assigned a polymeric structure with protons that bridge planar C₅(CN)₅ units.

Synthesis

Pentacyanocyclopentadiene is synthesised by coupling

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is an inorganic compound with the chemical formula and structure . It is also considered as the anhydride of thiocarbonic acid. It is a colorless, flammable, neurotoxic liquid that is used as ...

and

sodium cyanide Sodium cyanide is a compound with the formula Na C N and the structure . It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also expl ...

dimethylformamide Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for 2,5-dimethylfuran, dimethylfuran, or dimethyl fumarate), this colourless liqui ...

before

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

using

ammonium persulfate Ammonium persulfate (APS) is the inorganic compound with the formula (NH4)2S2O8. It is a colourless (white) salt that is highly soluble in water, much more so than the related potassium salt. It is a strong oxidizing agent that is used as a cataly ...

and final purification generates the ammonium pentacyanocyclopentadiene salt. Further reaction with

sodium hydride Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in co ...

generates NaC₅(CN)₅ which is a starting point for its coordination chemistry with transition metals.

Reactions and coordination chemistry

Coupling of sodium pentacyanocyclopentadiene (NaC₅(CN)₅) with transition metal halide salts generates metal complexes containing the anion. Because the anion binds to metals through the

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

group it can act as a pentagonal node, unlike most

cyclopentadienyl complex A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl groups (, abbreviated as Cp−). Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (''η''5-) bonding mode. The metal–cyclopentadien ...

es that bind to the face of the cyclopentadienyl ring. Thus it can form

fullerene A fullerene is an allotropes of carbon, allotrope of carbon whose molecules consist of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to six atoms. The molecules may ...

-like structures with large voids containing solvent. This has important implications for gas storage and separation.

References

{{reflist Nitriles Cyclopentadienes Superacids