On the structure refinement of metal complexes against 3D electron diffraction data using multipolar scattering...

Area of Science:

• Crystallography
• Materials Science
• Computational Chemistry

Background:

• Accurate electron density modelling is crucial for crystal structure refinement, especially for organometallic complexes.
• Traditional methods like the independent atom model (IAM) may not fully capture the electron density distribution in complex structures.
• 3D electron diffraction (3D ED) offers a powerful tool for determining crystal structures, but its accuracy depends on reliable scattering factor models.

Purpose of the Study:

• To investigate and compare different electron density modelling methods for refining organometallic complexes using 3D ED data.
• To evaluate the effectiveness of the transferable aspherical atom model (TAAM) against the IAM for iron(III) complexes.
• To assess the impact of accurate scattering factor modelling on electrostatic potential and structural refinement.

Main Methods:

• Refinement of iron(III) acetylacetonate (FeAcAc) using both IAM and TAAM approaches.
• TAAM refinement utilized multipolar parameters and custom-derived scattering factors from DFT calculations for Fe-O coordination.
• Comparison of refinement results based on R1 values, goodness-of-fit (GooF), and Fourier difference maps for both 3D ED and SCXRD data.

Main Results:

• TAAM significantly improved crystal structure refinement for both 3D ED and SCXRD data, evidenced by lower R1 values and better GooF.
• TAAM provided a more accurate representation of the electron density and electrostatic potential compared to IAM, especially for the iron(III) center.
• Improvements were most pronounced in the low-resolution data range for 3D ED, indicating better modelling of electron distribution.
• TAAM refinement resulted in more realistic thermal ellipsoids, aligning better with SCXRD results.

Conclusions:

• The transferable aspherical atom model (TAAM) is highly effective for improving the crystal structure refinement of organometallic complexes using 3D electron diffraction (3D ED) data.
• Accurate modelling of electron density and scattering factors, particularly for metal centers, is essential for reliable structural analysis with 3D ED.
• TAAM offers a promising approach for detailed charge distribution analysis in complex molecular structures, enhancing the capabilities of 3D ED.