Crystallographic report: Crystal structure and quantum mechanical calculations on FOX-7, 1,1-diamino-2,2-dinitroethylene

The crystal structure of 1,1-diamino-2,2-dinitroethylene (FOX-7) has been investigated by means of single-crystal X-ray diffraction studies. The experimental work was done in April 1997. The result from the investigation shows that FOX-7 has got a very interesting crystal structure which explains some of the interesting physical properties FOX-7 exhibits, e.g. low friction and dropweight sensitivity and the absence of a melting point. The crystal structure consists of slightly wrinkled layered sheets. These sheets can move with low friction against each other, and thus the heat evolved by friction is minimised. This process can be compared to graphite for example, which can act as lubricant. Within the layered sheets a large number of intermolecular hydrogen bonds are present, i.e. hydrogen bonds between the molecules. However, no hydrogen bonds are present between the layers. Typical for the FOX-7 molecule is the p-electron delocalisation, resulting in that the carbon-carbon double-bond is between a single-bond and a double-bond. This stabilises the molecule and contributes to the very good thermal stability of FOX-7. Quantum mechanical calculations on FOX-7 agree well with the X-ray diffraction data and verifies the delocalisation of the p-electrons. In order to get a good density value of FOX-7, powder X-ray diffraction studies were also done. The density obtained by powder X-ray diffraction is 1.8822(3) g·cm-1.