Acquiring Focus on Paramagnetic Single-Atom Sites with Fast Magic-Angle Spinning NMR.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Chemistry

Background:

• Characterizing paramagnetic sites in materials is crucial for understanding their properties.
• Traditional NMR methods can be challenging for paramagnetic systems due to broad shifts.

Purpose of the Study:

• To introduce and validate a novel approach for characterizing paramagnetic sites in materials.
• To elucidate the coordination geometry and electronic structure of an iron-containing metal-organic framework (MOF).

Main Methods:

• Combining broadband fast magic-angle spinning (MAS) NMR spectroscopy with ab initio computed paramagnetic NMR shifts.
• Utilizing correlated wave functions for accurate computational predictions.
• Analyzing 1H and 13C MAS NMR spectra of ligand atoms in a model Fe@PCN-224 MOF.

Main Results:

• The combined NMR and computational approach accurately predicted 13C NMR shifts for the paramagnetic Fe@PCN-224 MOF.
• The predictions showed excellent agreement with experimental data, even with a wide NMR shift range (1200 ppm).
• The method performed equally well for the diamagnetic counterpart (Fe-free PCN-224 MOF).

Conclusions:

• The developed approach is highly effective for characterizing paramagnetic sites in various materials.
• This method is applicable to crystalline, noncrystalline, and molecular systems.
• It provides a powerful tool for determining coordination geometry and electronic structure in paramagnetic materials.