Reliable measurements of dipole moments from single-crystal diffraction data and assessment of an in-crystal enhancement

Abstract

Using seven examples of high-quality data sets of amino acids it is shown that accurate molecular dipole moments can be obtained from experimental diffraction data. Recommendations for practical modeling choices are given when using the Hansen/Coppens multipole model. Multipole-model results, including those from invariom refinement, are found to be less accurate than results from a basis-set description. The question whether a molecular dipole-moment enhancement in the solid state is fact or artifact is studied by a number of techniques: A theoretical molecule embedded in a cluster of point-charges gives a substantial enhancement, in agreement with Hirshfeld atom refinement with point charges and dipoles. The experimental techniques, multipole refinement and wavefunction fitting, lead to smaller dipole-moment enhancements than the theoretical predictions. © 2012 Springer-Verlag Berlin Heidelberg.