Synthesis, characterization, thermal properties and theoretical investigation on Bis(guanidinium) 4,4′- Azo-1H-1,2,4-triazol-5-one

Abstract Bis(guanidinium) 4,4′-Azo-1 H -1,2,4-triazol-5-one [G 2 (ZTO)] was synthesized and characterized by X-ray single crystal diffraction, elemental analyzer and Fourier Transform Infrared (FT-IR) spectrometer. The result from X-ray single crystal diffraction indicates that G 2 (ZTO) crystallizes in the monoclinic space group P 2(1)/ c with parameters of a  = 4.779(2) A, b  = 9.081(4) A, c  = 14.676(6) A, α  = 90.00°, β  = 92.43(7)°, γ  = 90.00°, V  = 636.4(5) A 3 , Z  = 2, μ (Mo K α ) = 0.131, F (000) = 328, S  = 1.071, D c  = 1.640 g·cm −3 , R 1  = 0.0510 and wR 2  = 0.1389. Interestingly enough, its structure does not contain crystallization water, which is a unique characteristic in this material. Besides, the molecular geometry of the compound was optimized by using Density Functional Theory (DFT) method at B3LYP/6-31G (d, p) level in the ground state, revealing that the obtained geometric parameters are in accordance with the X-ray result of the structure. The experimental vibrational spectrum was compared with the calculated spectrum. Besides, molecular electrostatic potential (MEP) of G 2 (ZTO) was computed with the same method in gas phase, theoretically. The thermal properties of this compound were investigated by DSC, TG/DTG and micro-DSC methods. The results manifest that its thermal behavior can be divided into two main decomposition stages, the first intense decomposition peak temperature is 248.11 °C at the heating rate of 10 °C·min −1 , which is higher than that of RDX (219 °C) but slightly lower than that of G(ZTO)·H 2 O (252.08 °C). The constant-volume combustion heat (Δ c U ) of G 2 (ZTO), G(ZTO)·H 2 O and ZTO were determined and then the enthalpy of formation were calculated. The results show that G 2 (ZTO) possesses the highest standard molar enthalpy of formation, which may be explained by the fact that G 2 (ZTO) contains no water and possesses the highest nitrogen content in all guanidine salts. Moreover, the apparent activation energy ( E ), thermal stability and safety parameters ( T SADT , T TIT , T b ) were also calculated. Besides, the calculated thermodynamic functions ( ΔS ≠ , ΔH ≠ and ΔG ≠ ) for the main exothermic decomposition process of the title compound are 47.25 J·mol −1 ·K −1 , 169.20 kJ·mol −1 and 144.24 kJ·mol −1 , respectively.