Chemistry Reference
In-Depth Information
Reliable Measurements of Dipole Moments from
Single-Crystal Diffraction Data and Assessment
of an In-Crystal Enhancement
B. Dittrich and D. Jayatilaka
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 diffrac-
tion 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.
Keywords Single-crystal X-ray diffraction molecular dipole moment dipole-
moment enhancement multipole model wavefunction fitting hirshfeld-atom
refinement
Contents
1 Introduction . . . ................................................................................ 28
2 Experimental Datasets . ....................................................................... 30
2.1 Experimental Challenge: Hydrogen Scattering ........................................ 30
2.2 Experimental Challenge: Data Resolution . ............................................ 31
