Residual dipolar coupling between quadrupolar nuclei under magic-angle spinning and double-rotation conditions

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Quantum Mechanics
• Chemical Physics

Background:

• Residual dipolar couplings (RDCs) are valuable for structural elucidation in spin-1/2 NMR.
• Extracting similar information from quadrupolar nuclei is challenging due to broadened lineshapes.
• Existing methods struggle to fully characterize dipolar interactions between two quadrupolar nuclei.

Purpose of the Study:

• To develop a comprehensive theory for describing dipolar coupling between two quadrupolar nuclei in the frequency domain.
• To validate the theory using experimental NMR data under Magic-Angle Spinning (MAS) and Double-Rotation (DOR) conditions.
• To enable accurate determination of heteronuclear dipolar coupling constants and quadrupolar coupling constant signs.

Main Methods:

• Hamiltonian diagonalization in the frequency domain.
• Development of theory applicable to MAS and DOR conditions.
• Experimental validation using 11B and 35/37Cl NMR on B-chlorocatecholborane.

Main Results:

• The theory accounts for all terms in the dipolar Hamiltonian, which become partially secular.
• NMR lineshapes are sensitive to quadrupolar coupling constants and J coupling (including sign).
• Successful determination of heteronuclear dipolar coupling constants and the sign of the quadrupolar coupling constant.

Conclusions:

• The developed theory provides a robust framework for analyzing dipolar couplings between quadrupolar nuclei.
• This method overcomes limitations of previous approaches, enabling extraction of previously inaccessible parameters.
• The findings significantly advance the structural analysis capabilities of solid-state NMR for systems involving quadrupolar nuclei.