Crystal structure, energetic materials

Structure 20 and salts 115 and 116 are formed by condensation of nitric oxide with diethylmalonate. Arulsamy and Bohle warn that this new type of compact ring structure forms dense crystals, and compounds 20, 115, and 116 are potential energetic materials which decompose violently at high temperatures <2002AGE2089>. 

Analyses of the structures and properties of a large number of energetic materials reveal that a combination of amino and nitro groups in a molecule often leads to better thermal stability, lower sensitivity to shock and impact, and increased explosive performance because of an increase in crystal density. Such observations are attributed to both intermolecular and intramolecular hydrogen bonding interactions between adjacent amino and nitro groups. Some modern triazole-based explosives have been designed and synthesized with this in mind. 

This chapter will not provide reviews of density and structure prediction, but rather focus on our work and its emphasis on predictions for energetic materials. Because of the importance of crystal density in the performance of energetic materials, our initial efforts were directed to this area in general and to volume additivity techniques in particular. 

Summary and Challenges. Because of the expense, labor, time requirements and possible danger (both to personnel and the environment) of synthesizing new energetic materials, it is important to pre-select only materials which have the potential for substantially better performance than compounds currently in use. In this chapter, our procedures for crystal structure (and density) prediction were detailed. Crystal structure prediction provides an entry into other important areas such as sensitivity and crystal habit. 

The high explosive octahydro-l,3,5,7-tetranitro-l,3,5,7-tetrazocine (HMX, Fig. 1) is the energetic material in a number of high performance military explosive and propellant formulations [3], HMX exhibits three crystal polymorphs at ambient pressure denoted J3- [4,5], a- [6], and <5-FlMX [7] and listed in terms of stability with increasing temperature. At temperature T 550 K the crystalline structure become unstable and HMX begins to melt. The liquid phase of HMX is very unstable and therefore no direct measurements of... 

Azide compounds of hypervalent main group elements such as Si and Ge are also highly explosive [83,84], but their structures and energetics have not been widely explored. Quite recently, the crystal structure of the Si(N3)62 anion has been reported, which has 90% nitrogen content, enough to be a possible high-energetic material candidate[83,84]. It is noted that Si(N3)62 (E = Ge, Pb) have been synthesized and are structurally known [83],... 

The structure of high energetic materials - nitroazo(azoxy)furazans showing high crystal density and excellent energetic properties of detonation velocity and detonation pressure - has been studied by NMR spectroscopy [137, 139, 505, 508, 509, 511, 518, 519],... 

Oyumi, Y, Brill, T. B. and Rheingold, A. L. (1986a). Thermal decomposition of energetic materials. 9. Polymorphism, crystal structures, and thermal decomposition of polynitroazabicyclo [3.3.1]nonanes. J. Phys. Chem., 90,2526-33. [286]... 

An extended material of valence electron spatial correlations (VEC) had been analyzed (Schubert, 1964), when it became apparent that one correlation of valence electrons alone is not sufficient for the explanation of crystal structures of metallic phases. The outer core electrons had to be taken into consideration. This may best be seen from the crystal structure of indium (Fig. 4) The lattice matrix of In may be given in diagonal form ai = (4.59 4.59 4.95) A. The explicit lattice constants are needed for verification that the proposed VEC is acceptable. The VEC is aj = aAi(l, —1,0 1,1,0 0,0,3/2) and may be decomposed into the equations at = a j + a2 a2 = - aj + a2 a3 = 3 a3/2, which may be verified by means of Fig. 4. If a correlation lattice is inserted into a crystal structure, this does not mean that there are positions of increased electron density in the cell, it only gives the commensurability which is favorable energetically. It is easily verified that the number of valence electron places per cell is = 12 and is equal to the number of valence electrons in the cell given above = 12. The A1 type of the VEC had been inferred from the diamond struc-... 

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