Polymerization of Tetracyanoethylene under Pressure

Based on first-principles calculations, possible phase
transformations
in the molecular crystals of tetracyanoethyelene (TCNE) were investigated
at high pressures. Six new carbon nitride systems with one-, two-,
and three-dimensional structures were found. The predicted polymeric
and graphitic structures are semiconductors with energy gaps of 0.3–1.7
eV. The predicted three-dimensional solids are also semiconductors
with larger energy gaps between 1.8 and 2.2 eV with large bulk moduli
>188 GPa. The calculation results suggest two polymerization mechanisms.
Furthermore, inspired by the chemical vapor deposition experimentally
obtained results, the possibility of folding of the predicted one-dimensional
polymeric system into cylindrical molecular structures is considered.
Results show that TCNE polymers longer than 18.0 Å can form TCNE-cylinders.
Upon hydrogenation of the predicted TCNE-cylinders, they form very
stable TCNE-cucurbituril-like structures with energy gaps larger than
2.67 eV.