Proton distributions and hydrogen bonding in crystalline and glassy hydrous silicates and related inorganic materials: Insights from high-resolution solid-state nuclear magnetic resonance spectroscopy

Solid-state ¹H nuclear magnetic resonance (NMR) spectroscopy has developed into a versatile, high-resolution method for elucidating the detailed structures of both crystalline and amorphous materials. Here, we summarize our recent endeavors in applying this method to crystalline and glassy silicates and related inorganic materials. We first present updated correlations between ¹H chemical shift and O⋯O and H⋯O distances of O-H⋯O hydrogen bonds, derived from a comprehensive ¹H chemical shift database containing both original high-quality fast magic angle spinning (MAS) and two-dimensional combined rotation and multiple pulse spectroscopy (CRAMPS)-MAS NMR data and literature MAS NMR data for a large number of inorganic compounds, including phosphates, silicates, (oxy)hydroxides, borates, sulfates, and carbonates. These correlations may be used to estimate hydrogen-bonding distances for inorganic oxide materials of unknown structures. We then present case studies for the application of high-resolution two-dimensional ¹H CRAMPS-MAS NMR to unravel the order/disorder of proton distributions in crystalline high-pressure hydrous silicates. Finally, we summarize some of our results on the water speciation in hydrous (alumino)silicate glasses of a range of compositions obtained through comprehensive ¹H MAS NMR, and ²⁹Si-¹H and ²⁷Al-¹H double-resonance NMR experiments, and analyze them in the framework of a quasi-chemical model.