23Na MAS‐NMR and 1H MAS‐NMR Studies in the Hydro‐Sodalite System

Abstract

AbstractThe basic (x = 2, n = 4), (x = 2, n = 0) and the non‐basic (x = 0, n = 8), (x = 0, n = 0) species of the hydrosodalite system Na6+x[AlSiO4]6(OH)x · nH2O have been studied by 23Na MAS‐NMR and 1H MAS‐NMR techniques at 297 K. The spectra are discussed in terms of structural data, which are provided by X‐ray and neutron diffraction experiments on hydro‐sodalite phases of identical compositions. The 1H MAS‐NMR spectrum of the non‐basic phase Na6[AlSiO4]6 · 8H2O confirms the recent neutron diffraction data. The chemical shift of 4.2 ppm correlates to regular water molecules in the sodalite cage, which show hydrogen bonding to the framework oxygens. The 1H MAS‐NMR double peak spectrum of the basic hydro‐sodalite species Na8[AlSiO4]6(OH)2 · 4H2O correlates with the structural OH groupings (3.4 ppm) and with one proton per ß‐cage (—1.0 ppm) showing a significant magnetic shielding effect. The large diamagnetic shift (—6.5 ppm) of the resonance signal in the 1H MAS‐NMR spectrum of the hydroxy‐sodalite Na8[AlSiO4]6(OH)2 indicates substantial change in the chemical bond of the hydrogen atom upon dehydration of the tetrahydrate Na8[AlSiO4]6(OH)2 · 4H2O at 775 K. — The phases of the non‐basic hydro‐sodalites show 23Na chemical shifts of approximately —8 and —9 ppm for the octahedrally coordinated sodium atoms in the octahydrate (n = 8) and in the anhydrous (n = 0) sodalite, respectively. — The 23Na chemical shifts of the basic sodalites range from —0.6 to —5.6 ppm, and the species reveal considerable quadrupolar interactions. At least two types of sodium ions are registered in basic hydro‐sodalite (n = 4) in accordance with structure analysis.