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.

Graphical abstractYIt proves that [Mn(H2O)6](PA)2 2H2O (1) was the compound not the salt. We got the structures of Mn(IMI)2(H2O)4](PA)2 (2) and [Mn(IMI)6](PA)2 H2O (3). And compounds 2 and 3 were synthesized by different dropping ways. The energies of combustion of 2 and 3 are higher to those of RDX and HMX.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► It proves that [Mn(H2O)6](PA)2 2H2O (1) was the compound not the salt. ► We got the structures of Mn(IMI)2(H2O)4](PA)2 (2) and [Mn(IMI)6](PA)2 H2O (3). ► Two new compounds 2 and 3 were synthesized by different dropping ways. ► The energies of combustion of 2 and 3 are higher to that of RDX and HMX.