Multipole electron densities and atomic displacement parameters in urea from accurate powder X-ray diffraction

Area of Science:

• Crystallography
• Materials Science
• Quantum Chemistry

Background:

• Electron density determination is crucial for understanding chemical bonding.
• Traditionally limited to high-symmetry inorganic solids using powder X-ray diffraction (PXRD).
• High-quality single crystals are often unavailable for many molecular systems.

Purpose of the Study:

• To challenge the limitations of PXRD in electron density determination.
• To assess the feasibility of using PXRD for molecular systems.
• To model electron density in crystalline urea using the multipole method.

Main Methods:

• Utilized a bespoke vacuum diffractometer with imaging plates for data collection.
• Obtained high-quality structure factors from crystalline urea.
• Applied the multipole method for electron density modeling.

Main Results:

• Successfully determined high-quality structure factors for crystalline urea.
• Electron density and chemical bonding features were modeled.
• Results were compared with a high-quality synchrotron single-crystal study.

Conclusions:

• Powder X-ray diffraction is a viable method for electron density determination in simple molecular crystals.
• This technique expands the scope of electron density studies beyond high-symmetry inorganic solids.
• Offers an alternative when high-quality single crystals are not accessible.