NITRO OXYGEN...HALOGEN INTERACTIONS: A COMBINED CRYSTALLOGRAPHIC DATABASE AND AB INITIO MOLECULAR ORBITAL STUDY. Vanessa J. Hoy[a], Judith A. K. Howard[a], Frank H. Allen[b], Jos P. M., Lommerse[b] and Gautam R. Desiraju[c], [a] Department of Chemistry, University of Durham, South Rd., DURHAM, DH1, 3LE, U.K.; [b] C.C.D.C, 12 Union Rd., CAMBRIDGE, CB2 1EZ, U.K.; [c] School of Chemistry, University of Hyderabad, Central University PO, Hyderabad, 500046, India.

Recently it has been observed that the halogens, Cl, Br and I form mutual recognition motifs with nitro groups[1-3]. Interactions of this type are of interest because of their potential to act as substructural building blocks in crystal engineering applications[4]. The usefullnes of X...O2N interactions for this purpose is critically dependant on our ability to predict their occurance. In order to do that we must have some understanding of the nature and strength of the interaction.

A previous crystallographic database study of X...O2N interactions[1] revealed that there are three X...O2N bonding modes; a symmetric P type, a skew Q type and an asymmetric R type. However, the precise geometric and energetic differences between these three were not investigated further.

In view of the limited scope of the previous study and the recent improvments in the Cambrige Crystallographic Database System's[5] three dimensional search software we felt that it was appropriate to perform a more complete analysis of the crystallographic results relating to X...O2N interactions and additionally, to obtain quantitative estimates of the interaction energies involved. The results of this study, together with relevent new structural data, will be presented.

1 - Desiraju, G. R., Pedireddi, V. R., Sarma, J. A. R. P., Zacharias, D. E., Acta Chim. Hung., 1993, 130, 451.

2 - Allen, F.H., Goud, B. S., Hoy, V. J., Howard, J. A. K., Desiraju, G. R., J. Chem. Soc., Chem. Commun., 1994, 2729.

3 - Allen, F.H., Goud, B. S., Hoy, V. J., Howard, J. A. K., Thalladi, V. R., Desiraju, G. R., J. Chem. Soc., Chem. Commun., 1996, in press.

4 - Desiraju, G. R., Angew. Chem. Int. Ed. Engl., 1995, 34, 2311.

5 - Allen, F. H., Davies, J. E., Galloy, J. J., Johnson, O., Kennard, O., Macrae, C. F., Mitchell, E. M., Watson, D. G., J. Chem. Inf. Comput. Sci., 1991, 31, 204.