Tetracyanoethylene

Tetracyanoethylene (TCNE) is a crystalline solid with a melting point of 200 °C. DuPont researchers prepared it in 1957 by treating dibromomalononitrile with copper in boiling benzene. TCNE is an excellent electron acceptor and has been used to prepare organic superconductors.

In 2001, J. S. Miller and co-workers at the University of Utah (Salt Lake City) discovered that the TCNE radical anion forms a dianionic dimer. They believed that the dimer contains an unusual four-atom, two-electron bond that connects the four olefinic carbon atoms. Recently, Miller and colleagues used Raman spectroscopy to confirm the existence of the four-center bond.