Elucidation of the structure of the century old Ponzio and Gastaldi (P&G) compound

In 1913, by treating a solution of aminoguanidinium chloride with a stoichiometric amount of potassium hydroxide, and leaving the solution to slowly evaporate, a reddish violet, basic compound was obtained by Ponzio and Gastaldi (P&G) and attributed to the structure of the 3,6-diamino-1,2,4,5-tetrazine.1 Later on, in 1954, Chao Han Lin et al.2 disproved this attribution, through the unequivocal synthesis of the latter. Presently, a century from its discovery, we report the elucidation of the structure of 1,1,4,10,10-pentaamino-2,3,5,6,8,9-hexaazadecan-1,3,5,7,9-pentaene, the P&G compound. Chemical and spectral studies have been done in order to advance a reasonable hypothesis for its formulation, whereas the structure has been determined by ab-initio X-ray powder diffraction analysis (XRPD). Moreover, in order to add, otherwise missing, information to our ab-initio XRPD structure determination, we have performed a lattice-constrained PBC-DFT optimization of our structural model. In this contribution, our results on the elucidation of the still-missing structure of the P&G compound will be presented.