Combined X-ray powder diffraction and DFT calculation to elucidate molecular and crystal structure of fluorostyrenes
M. Brunelli1, M.R. Johnson2 and
A.N. Fitch1,3
1 European Synchrotron Radiation Facility, B.P. 220, F38043 Grenoble Cedex France
2 Institute Laue Langevin, B.P. 156, F38042 Grenoble Cedex 9 France
3 Department of Chemistry, Keele University, Staffordshire, ST5 5BG, UK.
An example will be presented in which combination of structural
and numerical studies was applied to the investigation of the planarity of some
fluorine derivative of styrenes, fluorostyrenes. The interest in this detail of the molecular geometry of
fluorostyrenes came from some recent publications, [1, 2] in which a very
complete study of both the 3 and the 4 conformers were carried out using IR,
Raman, INS (Inelastic Neutron Scattering Spectroscopy) data combined with theoretical
calculations. DFT (Density Functional Theory) calculations on the free molecule
yield to the conclusion that these molecules are planar, while MO (Molecular Orbital)
calculation might give torsions angle different from 0 or 180, which is a
non-planar structure. In particular, in the INS data collected at 20 K, which
is in the solid phase, some discrepancy could be observed between the observed and the
calculated spectra at high wavenumbers. Therefore, more accurate DFT
calculations required to be performed in a periodic system and hence
information about their condensed state was needed.
We've performed a systematic study of the solid state structure of 2-, 3-, 4- fluorostyrene using X-ray powder diffraction in combination with numerical calculation. The measurements were performed at the high resolution powder diffraction beamline, ID31, at the ESRF, Grenoble (France). After solification of the samples (at around 220 K, 212 K and 245 K, respectively), no more phase changes were observed in the temperature range 295 - 12 K. The three fluorostyrenes ware found to have orthorhombic crystal structure at low temperature.
Here we report the final optimized valued for the torsion angle from the DTF-VASP calculations, of 3- and 4- fluorostyrene. The results suggest that the three fluorostyrenes in the solid state have torsion angle different from zero.
[1] J.M. Granadino-Roldan, M. Fernandez-Gomez, A. Navarro, L.M. Camus and U.A. Jayasooriya. Phys. Chem. Chem. Phys, 4 (2002) 4890-4901.
[2] J.M. Granadino-Roldan, M. Fernandez-Gomez, A. Navarro
and U.A. Jayasooriya. Phys. Chem. Chem. Phys. 5 (2003) 1760-1768.