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. In this feature article, 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 MAS and 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 (Fig. 1). These correlations may be used to estimate hydrogen-bonding distances for inorganic 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 concerning 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 (Fig. 2).
“This is likely to become a “classic”, often-cited paper, because it covers so much.”--Reviewer (30, Nov., 2009)
Xue, X., Kanzaki, M., Proton distributions and hydrogen bonding in crystalline and glassy hydrous silicates and related inorganic materials: insights from high-resolution solid-state NMR spectroscopy. J. Am. Ceram. Soc., 92, 2803-2830, 2009. Abstract (InterScience)
Figure 1 Correlation between 1H chemical shift and O···O distance for O-H···O hydrogen bonds in (oxy)hydroxides, phosphates, silicates, sulfates, borates and carbonates.
Figure 2 MOH/(SiOH+MOH) abundance ratio as a function of bulk MO/(MO+2SiO2) (fraction of oxygen atoms from the MO component in the anhydrous composition) for a series of hydrous glasses in the CaO-MgO-SiO2 system with 1~2 wt% water, derived from 1H MAS NMR data. Also shown are a series of curves calculated from a quasi-chemical model.
Figure 3 Cover page of the issue showing the crystal structure of superhydrous B described in this feature article.