Chemical bonding and intermolecular interactions in energetic materials: 1,3,4-trinitro-7,8-diazapentalene.

The electron density and related properties of the red-colored energetic material 1,3,4-trinitro-7,8-diazapentalene (space group Pca2(1)) have been determined from a low-temperature [90.0 (1) K] X-ray diffraction experiment. Intensity data were measured with a 2 K CCD Bruker diffractometer using Ag Kalpha radiation. One detector setting, several varphi settings, 0.15 degrees omega scans and 96 s exposure time per frame gave R(int) = 0.0188 for 31 952 (10 283 unique) reflections and (sin theta/lambda)(max) = 1.15 A(-1). The electron density was modeled using the Hansen-Coppens [(1978), Acta Cryst. A34, 909-921] multipole model and refined to R = 0.026 for 9455 unique observed reflections. The electron density, Laplacian and electrostatic potential distributions are reported and discussed. The properties of the bond (3,-1) critical points are analyzed. All results are indicative of multiple bonds in the five-membered rings. In addition, a significant number of weak intermolecular interactions (O...H, O...O, O...N, O...C) have also been characterized by the properties of their critical points. A comparison of experimental results with those obtained from theoretical calculations (periodic, CRYSTAL98; single molecule, GAUSSIAN98) is also reported.