Tetracyanomethane

Tetracyanomethane or carbon tetracyanide is an organic compound with the chemical formula C(CN)4. It is a percyanoalkane. It is a molecular carbon nitride. The structure can be considered as methane with all hydrogen atoms replaced by cyanide groups. It was first made by Erwin Mayer in 1969.

Properties
Tetracyanomethane is a solid at room temperature. It decomposes over 160 °C without melting, and although it can be in a dilute vapour, no liquid form is known. The molecules of tetracyanomethane have a tetrahedral symmetry (3m or Td). The molecule has C-C distance of 1.484 Å and C-N distance of 1.161 Å in the gas form. In the solid the C≡N bond shortens to 1.147 Å. The C-C bond has a force constant of 4.86×105 dyn/cm which is slightly greater than the C-Cl bond in carbon tetrachloride, but a fair bit weaker than in the tricyanomethanide ion. At pressures over 7 GPa tetracyanomethane starts to polymerize to form a disorganised covalent network solid. At higher pressure the white colour yellows and darkens to black. Over 20 GPa the polymerization is total.

The bulk modulus K0 = 4.4 and its derivative K0' = 18.

Production
Tetracyanomethane can be made by reacting cyanogen chloride with silver tricyanomethanide.


 * ClCN + AgC(CN)3 → C(CN)4 + AgCl

Reactions
In an acid solution in water tetracyanomethane is hydrolysed to yield tricyanomethanide and ammonium ions along with carbon dioxide. In alkaline solutions tricyanomethanide and cyanate ions are produced.