Chemical bonding in energetic materials: beta-NTO.

The electron density and related properties of the quasi-stable beta form of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO; space group P2(1)/c) have been determined from a low-temperature [100 (1) K] X-ray diffraction experiment. Intensities were measured with a 2K CCD Bruker diffractometer using Ag Kalpha radiation. Two detector settings, several varphi settings, 0.3 degrees omega scans and 160 s exposure time per frame gave R(int) = 0.0215 for 68 989 (4080 unique) reflections and (sin straight theta/lambda)(max) = 1.23 A(-1). The Hansen-Coppens [Acta Cryst. (1978), A34, 909-921] multipole model as implemented in the XD program gave R = 0.0333 (all reflections), which allowed calculation of the electron density, Laplacian and electrostatic potential distributions. The bonding (3,-1) critical points and the molecular dipole moment of 3.2 (1) D were also obtained. Chemical bonding in the molecule is discussed.