Solid-state NMR of a paramagnetic DIAD-FeII catalyst: sensitivity, resolution enhancement, and structure-based...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Characterization
• Catalysis

Background:

• Paramagnetic molecular solids pose challenges for structural characterization due to broad NMR resonances and short relaxation times.
• Solid-state NMR is a powerful technique for atomic-level structural determination of materials.

Purpose of the Study:

• To develop a general protocol for the structural characterization of paramagnetic molecular solids using solid-state NMR.
• To demonstrate the protocol's effectiveness on a high-spin Fe(II) catalyst precursor.

Main Methods:

• Utilizing very fast magic angle spinning (MAS) (>30 kHz) on natural abundance powder samples.
• Optimizing broadband heteronuclear (proton-carbon) recoupling sequences for efficient polarization transfer.
• Employing single or multiple quantum correlation NMR experiments to mitigate bulk magnetic susceptibility (BMS) broadening.
• Combining NMR data with density functional theory (DFT) calculations for resonance assignment.

Main Results:

• Achieved good NMR performance despite anisotropic shifts and short relaxation times.
• Successfully optimized polarization transfer and developed methods to overcome magnetic susceptibility broadening.
• Obtained detailed structural insights into the Fe(II) catalyst precursor.

Conclusions:

• The developed solid-state NMR protocol is effective for characterizing paramagnetic molecular solids.
• Fast MAS and advanced NMR techniques enable detailed structural analysis of challenging samples.
• This approach facilitates the structural elucidation of catalytic materials.