4,10-Diformyl-2,6,8,12-tetranitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.05,9.03,11]dodecane

The title compound TNDFIW, C8H8N10O10, is a caged heterocycle substituted with four nitro and two formyl groups. It is related to the hexaazaisowurtzitane family of high-density high-energy polycyclic cage compounds. Four nitro groups are appended to the four N atoms of the two five-membered rings, while the other two formyl groups are attached to the two N atoms of the six-membered ring, which adopts a boat conformation. The compound has a cage structure which is constructed from one six-membered and two five-membered rings which are closed by a C—C bond, thus creating two seven-membered rings. There are a number of close intermolecular contacts [O⋯O = 2.827 (5), 2.853 (4) and 2.891 (5) Å; O⋯N = 2.746 (2) and 2.895 (2) Å] The calculated density of TNDFIW is 1.891 Mg m−3.

The caged structure of HNIW is constructed from one six-membered and two five-membered rings which are closed by the C1-C4 bond, thus creating two seven-membered rings.The six-membered pyrazine ring has a boat conformation, while the more stable conformation of a six-membered ring is the chair form. Four nitro groups are appended to the four nitrogen atoms of the two five-membered rings, while two formyl groups are attached to the two nitrogen atoms of the six-membered ring. Due to caged structure of TNDFIW, the N-N (1.374-1.43 Å) bond length is much longer than that found in common nitramines (1.360 Å). The C-C bond lengths of TNDFIW (1.56-1.59 Å) are also much longer than normal C-C single bonds (1.54 Å). Bond angles in caged structures are also usually much larger than normal sp3 hybrid bond angles (Zarychta et al., 2005). There are a number of close intermolecular contacts less than the van der Waals radii, such as O1···O3 (2.827 Å), O6···O8 (2.853 Å), O2···O4 (2.891 Å); O2···N9 (2.895 Å), and O8···N9 (2.746 Å). From the above analysis, we know that TNDFIW has high tensile force and energy.

Experimental
Due to the higher electronic density of five-membered rings than six-membered rings, N atoms on the 2, 6, 8, 12-positions of the two five-membered rings are more reactive than the N atoms on the 8 and 10-positions of the six-membered ring.
Therefore, the four acetyls on on the five-membered rings are cleaved first and replaced by nitro groups in the nitrolysis of TADFIW with mixed sulfuric and nitric acids as the nitrating agent.
Fuming sulfuric acid was slowly added into fuming nitric acid in a three-neck flask with stirring. After the solution of mixed acids was heated to 40 0 C, tetraacetyl-diformylhexaazaisowurtzitane (10 g) was added, and then the temperature was elevated to 45 0 C. The solution was maintained at 45 0 C for 8 h; thereafter the solution was poured into ice-water.
The precipitated solid was filtered off, washed with water and then dried. The obtained solid was a mixture of polynitrohexaazaisowurtzitane derivatives with different numbers of nitro substitutes.
Pure TNDFIW was obtained using silica column chromatography with hexane/acetyl acetate (6/4 by volume) as the mobile phase at room temperature (25 0 C). Pure TNDFIW was dissolved in dry acetyl acetate, and then several drops of hexane was added. The resulting solution wasallowed to sit at ambient conditions (15-20 o C). A week later, single crystals supplementary materials sup-2 was obtained by controlling the evaporation of the solvent. Element analysis, FT-IR, MS and 1 H NMR were in agreement with the structure of TNDFIW.

Refinement
All non-hydrogen atoms were obtained using the direct methods. The hydrogen atom were placed geometrically and treated by a constrained refinement. The distances of C1-H, C2-H,C3-H,C4-H,C5-H, C6-H are 1.000 A, and the distance of C7-H is 0.950 A. The U eq of H is assigned 1.2 time U eq of C linked. Since the absolute configuration for the compound could not reliably be determined from Mo Kα; data, the Friedel equivalents were merged before the final cycles of refinement.