Tetracyanomethane under Pressure: Extended CN Polymers from Precursors with Built-in sp3 Centers

Abstract

Tetracyanomethane, C(CN)₄, is a tetrahedral molecule containing a central sp³ carbon that is coordinated by reactive nitrile groups that could potentially transform to an extended CN network with a significant fraction of sp³ carbon. High-purity C(CN)₄ was synthesized, and its physiochemical behavior was studied using in situ synchrotron angle-dispersive powder X-ray diffraction (PXRD) and Raman and infrared (IR) spectroscopies in a diamond anvil cell (DAC) up to 21 GPa. The pressure dependence of the fundamental vibrational modes associated with the molecular solid was determined, and some low-frequency Raman modes are reported for the first time. Crystalline molecular C(CN)₄ starts to polymerize above ∼7 GPa and transforms into an interconnected disordered network, which is recoverable to ambient conditions. The results demonstrate feasibility for the pressure-induced polymerization of molecules with premeditated functionality.