Potassium hydrogen disilicate: A possible model compound for17O NMR spectra of hydrous silicate glasses

Abstract

Oxygen-17 magic angle spinning, non-spinning, 1 H-decoupled, 1 H- 17 O cross-polarization, and triple-quantum magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy experiments were performed at two different magnetic fields on crystalline potassium hydrogen disilicate (KHSi 2 O 5 ) and hydrous and anhydrous potassium tetrasilicate (K 2 Si 4 O 9 ), sanidine (KAlSi 3 O 8 ), and haplogranite (KAlSi 3 O 8 -NaAlSi 3 O 8 -SiO 2 ) glasses. Crystalline KHSi 2 O 5 has two bridging oxygen sites and one non-bridging oxygen site, and the NMR parameters for these two types of sites have been determined. The non-bridging oxygen (silanol) site is well-resolved and observed in a crystalline compound with an isotropic chemical shift (δ iso ) of 60 ppm, a quadrupolar coupling constant (C Q ) of 3.5 MHz, and an asymmetry parameter (η) of 0.35. Knowledge of the non-bridging-oxygen site parameters allows for comparisons to glassy or other materials that might have silanol-type structures. A similar peak can be found in the hydrous potassium silicate spectrum but not in the hydrous potassium aluminosilicate glass spectrum.