Solving the Hydrogen and Lithium Substructure of Poly(triazine imide)/LiCl Using NMR Crystallography

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photocatalysis

Background:

• Poly(triazine imide) with incorporated lithium chloride (PTI/LiCl) shows promise for photocatalytic water splitting.
• A significant challenge is the H/Li disorder, hindering structure-property relationship elucidation, particularly for band-gap tuning.

Purpose of the Study:

• To resolve the complex H/Li substructure within PTI/LiCl.
• To establish clear structure-property correlations for optimizing photocatalytic applications.

Main Methods:

• Utilized a synergistic combination of multinuclear solid-state NMR spectroscopy (1D and 2D), chemical modeling, automated electron diffraction tomography, and X-ray pair distribution function analysis.
• Employed advanced analytical techniques to overcome the limitations of previous structural studies.

Main Results:

• Successfully delineated the H/Li substructure, identifying specific hydrogen atom bonding sites and lithium ion positions within the cavities.
• Revealed that local dipole moments induce framework buckling and Cl- ion displacements, with a coherence length below 2 nm.
• Confirmed the average structure conforms to space group P212121.

Conclusions:

• The combined analytical approach provides a powerful strategy for resolving intricate substructures in materials like PTI/LiCl.
• Understanding the precise H/Li arrangement is crucial for tailoring the material's photocatalytic properties and band-gap characteristics.