Preparation, crystal structures and thermal decomposition of three energetic manganese compounds and a salt based on imidazole and picrate

The multi-ligand coordination compound of [Mn(H₂O) ₆](PA)₂·2H₂O (1), [Mn(IMI) ₂(H₂O)₄](PA)₂ (2) and [Mn(IMI) ₆](PA)₂·H₂O (3), and a salt of (IMI)(PA)·H₂O (4) were synthesized by using imidazole (IMI) and picrate (PA). Furthermore, they were characterized by elemental analysis and FT-IR spectrum. The crystal structures were determined by X-ray single crystal diffraction. The obtained results show the crystals of 1 and 4 belong to orthorhombic, Pccn and Pna2₁ space groups, and the crystals of 2 and 3 belong to monoclinic, P2₁/c space groups. The metal Mn(II) cations are six-coordinated and exhibit distorted-octahedral configuration. Under nitrogen atmosphere with a heating rate of 10 K min^-1, the thermal decompositions contain two main exothermic stages in the DSC curves corresponding to TG-DTG curves. The non-isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa's method, respectively. The energies of combustion, enthalpies of formation, critical temperatures of thermal explosion, entropies of activation (ΔS^≠), enthalpies of activation (ΔH^≠), and free energies of activation (ΔG^≠) were measured and calculated. In the end, the sensitivity properties were also determined with standard methods.