10-Formyl-2,4,6,8,12-pentanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.03,11.05,9]dodecane

The title compound, C7H7N11O11 (PNMFIW), is a caged heterocycle substituted with five nitro and one 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 a nitro group and a formyl are attached to the two N atoms of the six-membered ring.

The title compound, C 7 H 7 N 11 O 11 (PNMFIW), is a caged heterocycle substituted with five nitro and one 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 a nitro group and a formyl are attached to the two N atoms of the six-membered ring.

Comment
The title compound, pentanitromonoformylhexaazaisowurtzitane (PNMFIW), was reported as a by-product in the synthesis of hexanitrohexaazawurtzitane (HNIW) (Golfier et al., 1998;Liu et al.,2006). We theoretically studied PNMFIW with quantum calculation and found that PNMFIW has a similar crystal structure and density but lower sensitivity compared with HNIW (Wu et al., 2003). The crystal structure of an energetic compound is very important, because detonation performance such as detonation velocity and pressure, depends largely on density which is identified by its crystal structure, while the sensitivity closely correlates with the crystal structure (Singh et al., 2003;Zeman et al., 2003). To now, the crystal structure and properties of PNMFIW have not been reported. We synthesized PNMFIW through the nitrolysis of tetraacetyldiformylhexaazaisowurtzitane (TADFIW) in mixed nitric and sulfuric acids and obtained single crystals of PNMFIW by controlled evaporation.
The main geometric parameters of PNMFIW are listed in Tables 1 and 2, and the molecular structure is illustrated in Fig.1.
The cage structure of PNMFIW 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 in PNMFIW boat-shaped , while more stable conformation of six-membered ring is in the chair form. The two five-membered rings are also non-planar, being characterized by the torsion angles of two five-membered rings. Four nitro groups are appended to the four nitrogen atoms of the two five-membered rings, while a nitro group and a formyl are attached to the two nitrogen atoms of the six-membered ring respectively. Due to cage structure of PNMFIW the bond length of N-N (1.369-1.436 Å) is much longer than common nitramine (1.360 Å). The bond length of C-C (1.561-1.587 Å) of PNMFIW is also much longer than common C-C bond (1.54 Å). Bond angles of N(4)-C(5)-C(6) (112.7°), C(7)-N(1)-C(1)(122.2°) and C(2)-N(2)-C(3) (117.5°) on caged structure are much bigger than normal angle of sp 3 hybrid bond. From the molecular structure analysis above, we know that PNMFIW molecule has high tensile force and energy.

Experimental
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 60 °C, tetraacetyldiformylhexaazaisowurtzitane (10 g) was added, and then the temperature was elevated to 65 °C. The solution was maintained at 65 °C for 12 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 number of nitro substitutes. Pure PNMFIW was obtained through a silica column chromatography with hexane/acetyl acetate (6/4 by volume) as mobile phase at room temperature (25 °C).
Pure PNMFIW was dissolved in mixed solvents of acetone and n-hexane, and then the resulted solution was placed in ambient condition (288-293 K). A week later, single crystals was obtained by controlling the evaporation of solvent.
Elemental analysis, FT-IR, MS and 1 H NMR are in agreement with the structure of PNMFIW.
supplementary materials sup-2 Refinement All non-hydrogen atoms were obtained from the difference Fourier map and refined with atomic anisotropic thermal parameters. The hydrogen atoms were placed geometrically and treated a constrained refinement. All C-H distances are constrained to 1.00 Å, except C7-H7 which is 0.95 Å. In all cases U eq (H) = 1.2U eq (C). Friedel pairs were merged during final refinement owing to the lack of anomalous dispersion data. Fig. 1. The structure of PNMFIW with displacement ellipsoids drawn at the 50% probability level. 4,6,8,4,6,8,10,11