Energetic materials that can be used for propellants and explosives need to combine safety and stability with a high energy density and, if possible, a low environmental impact. A high nitrogen content leads to good explosion characteristics and to the production of environmentally friendly N2 during the decomposition of the materials.
Pengcheng Wang, Ming Lu, Nanjing University of Science and Technology, China, and colleagues have synthesized an entirely inorganic zinc(II) complex that could be used as an environmentally friendly energetic material. The team combined [Na(H2O)(N5)]∙2 H2O and Zn(NO3)2∙6 H2O to form the desired complex [Zn(H2O)4(N5)2]∙4 H2O in an ion metathesis reaction. The pentazole anion (N5–, pictured) in the product is coordinated to the central zinc ion via one nitrogen atom, and the remaining four coordination sites are occupied by water molecules.
The researchers characterized the compound using X-ray crystallography, infrared (IR) and Raman spectroscopy, and differential scanning calorimetry (DSC). The water molecules interact with both the Zn(II) cation and the pentazole anions and contribute significantly to the stability of the complex. The decomposition of the compound starts at temperatures of about 108 °C, which indicates a good thermal stability and could allow the safe use as a high-energy density material.
- A Carbon-free Inorganic-metal Complex Consisting of All-nitrogen Pentazole Anion, Zn(II) Cation and H2O,
Yuangang Xu, Pengcheng Wang, Qiuhan Lin, Ming Lu,
Dalton Trans. 2017.