Tetracyanomethane or carbon tetracyanide is an organic compound with the chemical formula . 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.
Tetracyanomethane is a solid at room temperature. It decomposes over 160 ðC 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 T<sub>d</sub>). The molecule has C-C distance of 1.484 àand C-N distance of 1.161 àin the gas form. In the solid the Câ¡N bond shortens to 1.147 à. The C-C bond has a force constant of 4.86ÃÂ10<sup>5</sup> 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 K<sub>0</sub> = 4.4 and its derivative K<sub>0</sub>' = 18.
Tetracyanomethane can be made by reacting cyanogen chloride with silver tricyanomethanide.
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.