Quadruple azidation of 2,4,6,8-tetrachloropyrimido[5,4-d] pyrimidine gave tetraazidopyrimido[5,4-d]pyrimidine (C6N16) with 86% yield. The title compound undergoes azide–tetrazole tautomerism in neutral organic solvents, but exists as a protonated C2-symmetric tetraazide dication in trifluoroacetic acid. On the other hand, in the solid state it occurs as a monotetrazole tautomer as revealed by its single crystal X-ray analysis. The newly obtained binary compound C6N16 is very sensitive towards both impact (<1 J) and friction (1 N). A detonation velocity of 7477 m s−1 with a 20.8 GPa detonation pressure was calculated using the EXPLO5 code (version V7.01.01).