Polymorphism of bimolecular crystals of CL-20 with tris[1,2,5]oxadiazolo[3,4-b:3´,4´-d:3″,4″-f]azepine-7-amine

Abstract

New bimolecular crystals (BMCs) of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) with tris[1,2,5]oxadiazolo[3,4-b:3´,4´-d:3″,4″-f]azepine-7-amine (AZ2) were synthesized. Four different crystal structures — two polymorphic modifications with the CL-20: AZ2 ratio of 1: 1 (BMCs 1 and 2) and two polymorphic modifications with the ratio of 1: 2 (BMCs 3 and 4) — were obtained depending on the crystallization conditions. These crystals were studied by X-ray diffraction. The results of quantum chemical calculations indicate that the new η-conformation found in crystal 1 is not a stable conformer of CL-20 and its existence is attributed to the crystal packing effects in structure 1.