High field (33)S solid state NMR and first-principles calculations in potassium sulfates

Area of Science:

• Solid-state NMR Spectroscopy
• Quantum Chemistry
• Inorganic Chemistry

Background:

• Potassium sulfates exhibit diverse sulfur chemical environments.
• Studying sulfur-33 (33S) presents challenges due to low natural abundance and small gyromagnetic ratio.

Purpose of the Study:

• To investigate various sulfur environments in potassium sulfates (K(2)SO(4), KHSO(4), K(2)S(2)O(7), K(2)S(2)O(8)) using high-field solid-state NMR.
• To assign NMR signals and determine electric field gradient (EFG) tensor orientations.
• To assess the utility of computational methods in interpreting experimental NMR data.

Main Methods:

• High-field (21 T) solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence.
• Quantum mechanical calculations using Gaussian 98 (density functional theory) and CASTEP (periodic boundary conditions, projector-augmented wave).

Main Results:

• Good quality (33)S solid-state NMR signals were obtained for potassium sulfates, even with low natural abundance.
• The QCPMG technique enabled detection of sites with quadrupole coupling (C(Q)) values up to 16 MHz.
• Computational methods provided valuable assistance in assigning NMR sites and understanding EFG tensor orientations, despite only semiquantitative agreement with experimental parameters.

Conclusions:

• Solid-state (33)S NMR, enhanced by the QCPMG technique, is effective for characterizing sulfur environments in inorganic compounds.
• Quantum chemical calculations serve as a crucial tool for interpreting complex solid-state NMR spectra.
• This study demonstrates a synergistic approach combining experimental NMR and computational chemistry for detailed structural analysis.