TOPOLOGICAL PROPERTIES OF ELECTRON DENSITY OF PENTAFLUOROSULFANYL DERIVATIVES. G. J. Perpetuo, T. Koritsanszky, D. Preugschat, D. Lentz and P. Luger, Institute for Crystallography and Institute for Inorganic Chemistry Free University of Berlin, Germany

Topological analyses of experimental and theoretical electron densities and Laplacian functions of the title compounds (SF5X, X = NC, NCO and CN) are presented. The parameters of a static density model based on the multipole formalism /1,2/ has been extracted from high-resolution X-ray diffraction data collected at 120 K. Ab-initio calculations /3/ have also been performed at the Hartree-Fock and MP2 level of theory utilizing 6-311G+(3df) and 6-311G* basis sets, respectively. Geometry optimizations were also carried out. In the case of SF5NCO the asymmetric unit consists of two conformers; the isocyanate being in eclipsed and straggered position with respect to the equatorial SF4 moiety. Calculations at the MP2 level show the latter to correspond to a transitional state. The experimental bond-topological properties /4/ (the electron density and its Laplacian at the bond critical points) occur to be overestimated compared to those calculated from wavefunctions. The application of high basis sets including polarization and diffuse functions is proved to be important. The degree of the covalent character of the S-F bonds in the different molecules is compared.

/1/ N.K. Hansen and P. Coppens, Acta Cryst. A34, 909, 1978.

/2/ T. Koritsanszky, S. Howard, P.R. Mallinson, Z. Su, T. Richter and N.K. Hansen: XD a Computer Program Package for Multipole Refinement and Analysis of Electron Densities from Diffraction Data, 1995.

/3/ Gaussian 92/DFT, Revision G.4, J. A. Pople et al,Gaussian, Inc., Pittsburgh PA, 1993.

/4/ R.F.W. Bader, Atoms in Molecules: A Quantum Theory;Clarendon Press, Oxford, U.K., 1990.