Crystal engineering of energetic materials: co-crystals of Ethylenedinitramine (EDNA) with modified performance and improved chemical stability.

In the area of energetic materials, co-crystallization is emerging as a new technology for modifying or enhancing the properties of existing energetic substances. Ethylenedinitramine (EDNA) is a known energetic material which requires attention partly due to its chemical instability originating with its two highly acidic protons. In order to stabilize EDNA, a co-crystallization approach targeting the acidic protons using a series of co-crystallizing agents with suitable hydrogen-bond acceptors was employed. Fifteen attempted co-crystallizations resulted in eight successful outcomes and six of these were crystallographically characterized and all showed evidence of hydrogen bonds to the intended protons. Calculated detonation properties and experimental thermal and impact data for the co-crystals were obtained and compared with those of pure EDNA. The co-crystal of EDNA and 1,2-bis(4-pyridyl)ethylene was recognized as a more thermally stable alternative to EDNA while the co-crystal of EDNA and pyrazine N,N'-dioxide showed comparable detonation strengths (and much improved chemical stability) compared with that of EDNA. The co-crystals EDNA:4,4'-bipyridine and EDNA:pyrazine N,N'-dioxide were found to be about 50 % less impact sensitive than EDNA, all of which illustrate how co-crystallizations can be utilized for successfully modifying specific aspects of energetic materials.