This report describes the rapid and slow thermal decomposition of an energetically unstable polycyclic and heterocyclic azide, triazido-s-heptazine (C6N16), to produce nitrogen-rich CNx materials (x > 1.2). An analysis of gaseous byproducts shows that this large heterocyclic precursor releases primarily N-2 gas during its decomposition. The product composition and its morphology are dependent on the rapidity of the TAH decomposition. The CNx products are thermally stable to 500 degrees C and exhibit variations in H and O content dependent on precursor preparation and atmospheric exposure. The rapid decomposition of TAH leads to visibly porous powders, while slow decomposition yields smooth monoliths that are reminiscent of the morphology of the starting polycrystalline powder. IR and NMR spectral similarities between the amorphous CNx products and several previously reported heptazine molecules and extended heptazine networks supports significant retention of heptazine motif in these amorphous carbon nitride extended materials.