Determination of molecular conformation in the solid state without diffraction data

Abstract

A simple method for the determination of molecular conformations for molecules in molecular crystals based on inelastic neutron scattering (INS) vibrational spectra is described. This method is based on the dependence of low frequency vibrations on molecular conformation and the reliability of INS intensity calculations. Diffraction data is not required. The objective of the method is determination of the molecular structure for the solid state. It uses isolated molecule calculations to establish which conformation of the isolated molecule is the best approximation to the conformation present in the crystal. This is done by comparing the INS spectra computed for the isolated molecule model with the experimental spectrum. The direct relationship between the computed normal modes and INS intensity, in addition to the full coverage of the low frequency part of the spectrum, make INS the vibrational spectroscopy of choice for this method.

Acknowledgements

This work was supported by NSF grant CHE-0240104. We thank the ISIS facility of the Rutherford Appleton Laboratory, Chilton, UK for neutron beam time on the TOSCA spectrometer. We thank Sharon Rivera for her assistance in obtaining the spectrum of biphenyl.