CRYSTAL STRUCTURE AND DENSITY PREDICTION FOR FURAZANES AND CORRESPONDING FUROXANES

E.A. Arnautova¹, A.V. Dzyabchenko², T.S. Pivina³, and N.S. Zefirov¹

¹ Institute of Physiologically Active Compounds, Russian Academy of Sciences, Moscow region, Chernogolovka, 142432 Russia
² L.Ya. Karpov Institute of Physical Chemistry, ul. Vorontsovo Pole 10, Moscow 103064, Russia
³ N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky pr. 47, 117913 Moscow, Russia

Furazanes and their N-oxides (furoxanes) represent two very important classes of compounds which can be used for a wide set of applications: as components of pesticides, drugs, energetic materials, etc.

Compounds of these two classes are close to any other by their structure though they are noticeably different by their physical-chemical properties. Therefore the problem of a study and prediction of structure and properties of these compounds are of high interest both of theoretical and practical points of view.

We employed our original approach^[1] based on the Atom-Atom Potential Method to predict the crystal structure and density for a set of furazans and furoxanes. It is known that a major problem of calculations is the uncertainty which arises from the use of empirical models for the intermolecular interaction description. Especially valuable for the prediction of crystal structure and density are the methods that correctly describe electrostatic interactions and provide adequate estimation of relative stability of possible molecular packings as a result. Firstly we tested a set of interatomic potentials including different charge models in accordance with their ability to reproduce of known crystal structures and enthalpies of sublimation. A number of semi-empirical and ab initio MO methods were used to obtain charge distributions. Atomic charge models selected for them to fit with the calculated electrostatic potential surrounding were also considered. Then a global search for optimal packings of molecules under investigation was performed using PMC program (A.V. Dzyabchenko^[2],[3]) in most probable space groups with the use of no-charge and a different charge models.

As established, the observed crystal structures cannot be predicted by a simple no-charge model. The molecular packings found by the global search give a reasonably successful prediction of the crystal structure and density. The error of density calculation does not exceed 0.02 g cm^-3. Peculiarities of molecular packings of furazanes and furoxanes were examined and certain qualitative structure-property relationships were revealed.

^[1] Dzyabchenko A.V., Pivina T.S., Arnautova E.A. J. Mol. Struct., 378 (1996), 67.
^[2] Dzyabchenko A.V., Belsky V.K., Zorkii P.M. Kristallografiya, 24 (1979), 221 (in Russian).
^[3] Dzyabchenko A.V. Kristallografiya, 28 (1983), 788 (in Russian).