Metal salts of the 4,5-dicyano-2H-1,2,3-triazole anion ([C4N5]−)

Abstract

Diaminomaleodinitrile was reacted at low temperatures with in situ generated nitrous acid to form 4,5-dicyano-2H-1,2,3-triazole (1) in yields above 90%. Crystalline 1 was then reacted with one equivalent of a suitable alkali or alkaline earth metal base (typically a hydroxide or a carbonate) in a polar solvent to form the corresponding alkali and alkaline earth metal salts of 4,5-dicyano-2H-1,2,3-triazole (compounds 2-9). The thermal stability of the metal salts 2-9 was assessed by differential scanning calorimetry, which showed excellent thermal stabilities up to above 350 °C. Due to the energetic character of triazole-based salts, initial safety testing was used to assess the sensitivity of compounds 2-9 towards impact, friction, electrostatic discharge and fast heating. These results revealed very low sensitivities towards all four stimuli. Additionally, compounds 2-9 were characterized by mass spectrometry, elemental analysis, infrared and Raman spectroscopy and ((1)H, (13)C and (14)N) NMR spectroscopy. We also determined the solid state structure of the 4,5-dicyano-2H-1,2,3-triazole anion of one of the alkali metal salts (4: Monoclinic, P2(1)/c, a = 9.389(1) Å, b = 10.603(1) Å, c = 6.924(1) Å, β = 102.75(1)° and V = 1036.58(3) Å(3)) and one of the alkaline earth metal salts (6: Monoclinic, P2(1)/c, a = 9.243(1) Å, b = 15.828(2) Å, c = 6.463(1) Å, β = 90.23(1)° and V = 945.5(2) Å(3)). Furthermore, we noted the hydrolysis of one of the cyano groups of the 4,5-dicyano-2H-1,2,3-triazole anion in the strontium salt 8 to form the 5-cyano-2H-1,2,3-triazole-4-carboxylic acid derivative 8b, as confirmed by X-ray studies (8b: Monoclinic, P2(1)/n, a = 6.950(1) Å, b = 17.769(1) Å, c = 13.858(1) Å, β = 92.98(1)° and V = 1709.1(1) Å(3)). Lastly, we computed the NBO and Mülliken charges for the anion of compounds 2-9 and those of the anion of compound 8b.