Synthesis and structure of 2,5,8-triazido-s-heptazine: an energetic and luminescent precursor to nitrogen-rich carbon nitrides.

Derivatized s-triazine (C3N3) precursors have seen significant recent use in the production of carbon nitride materials. Larger polycyclic molecular precursors, such as those containing an s-heptazine core (C6N7 or tri-s-triazine), may improve stability and order in carbon nitride products. In this Communication, we describe the synthesis and crystal structure of 2,5,8-triazido-s-heptazine (2). Synthesis of 2 was achieved from melon, an oligomeric s-heptazine synthesized by the pyrolysis of NH4SCN. Melon was converted to molecular 2,5,8-trichloro-s-heptazine, which was then transformed to the triazide upon reaction with (CH3)3SiN3. The crystal structure of 2 verifies that the s-heptazine is planar and the azides adopt a pinwheel-like C3h arrangement around the periphery. The s-heptazine core shows pi delocalization in the C-N bonds around the periphery (av. 1.33 A), while the internal planar C-N bonds are longer (1.40 A). The heptazine units pack into parallel, but offset, layered sheets in the crystal. The triazide 2 exhibits photoluminescence at 430 nm and rapidly and exothermically decomposes upon heating at 185 degrees C to produce a tan thermally stable carbon nitride powder with a formula near C3N4.