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

Bis(guanidinium) 4,4'-Azo-1H-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 P2(1)/c with parameters of a = 4.779(2) angstrom, b = 9.081(4) angstrom, c = 14.676(6) angstrom, alpha = 90.00, beta = 92.43(7)degrees, gamma = 90.00 degrees, V = 636.4(5) angstrom(3), = 2, mu(Mo K-alpha) = 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 degrees C at the heating rate of 10 degrees C.min(-1), which is higher than that of RDX (219 degrees C) but slightly lower than that of G(ZTO)center dot H2O (252.08 degrees C). The constant-volume combustion heat (Delta U-c) of G(2)(ZTO), G(ZTO)center dot H2O 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 (Delta S-not equal, Delta H-not equal and Delta G(not equal)) 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. (C) 2017 Elsevier B.V. All rights reserved.