Atomic properties of N(2)O(4) based on its experimental charge density

Area of Science:

• Solid-state chemistry
• Crystallography
• Quantum chemistry

Background:

• Dinitrogen tetroxide (N2O4) exists as a dimer with a notably long N-N bond in its crystalline form.
• Understanding the electronic structure of such bonds is crucial for chemical bonding theories.

Purpose of the Study:

• To experimentally determine the charge density distribution and atomic properties of crystalline N2O4.
• To compare experimental findings with various theoretical calculations of atomic charges and volumes.
• To investigate the bond order of the long N-N bond in N2O4.

Main Methods:

• Low-temperature crystallization and X-ray diffraction using a CCD area detector.
• High-resolution data collection to generate experimental charge density.
• Application of Bader's Atoms in Molecules (AIM) theory to calculate zero-flux surfaces.
• Comparison of experimental data with theoretical calculations using Mulliken, AIM, NPA, and CHELP methods.

Main Results:

• Experimental charge density distribution was successfully generated for crystalline N2O4.
• Atomic volumes derived from experiment showed strong agreement with theoretical calculations.
• AIM charges demonstrated independence from the chosen basis set.
• A bond order of approximately 0.5 was estimated for the long N-N bond by comparing with model compounds.

Conclusions:

• The study validates the accuracy of theoretical methods in predicting atomic volumes, even for crystalline solids compared to isolated molecules.
• The long N-N bond in N2O4 exhibits a low bond order, suggesting a weak interaction.
• Experimental charge density analysis provides valuable insights into the nature of bonding in molecular crystals.