Dipole moment enhancement in molecular crystals from X-ray diffraction data

Area of Science:

• Crystallography
• Solid-state Chemistry
• Quantum Chemistry

Background:

• Determining molecular dipole moments from experimental charge density analyses in molecular crystals is challenging.
• However, experimental values are increasingly reported, necessitating systematic analysis.

Purpose of the Study:

• To collate existing experimental dipole moment data from crystal analyses.
• To identify trends and outliers in molecular dipole moment enhancement upon crystallization.
• To assess the potential of X-ray diffraction data for understanding crystal-induced charge distribution changes.

Main Methods:

• Compilation of all available experimental determinations of molecular dipole moments from crystal analyses.
• Analysis of the collated data to identify trends in dipole moment enhancement.
• Comparison of experimental findings with theoretical estimates.

Main Results:

• Molecular dipole moments derived from X-ray diffraction data provide significant information on charge distribution changes during crystal formation.
• A notable number of studies show considerable dipole moment enhancements (≥50%) in the crystal state.
• Specific cases exhibit enhancements of 100% or more, significantly exceeding theoretical predictions.

Conclusions:

• Experimental charge density analyses are a powerful, yet underutilized, tool for detailed study of crystal formation effects.
• Outlier cases with large dipole moment enhancements warrant further detailed experimental and theoretical investigation.
• The findings underscore the importance of experimental charge density studies for understanding solid-state phenomena.