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

Abstract

Abstract The 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 Na 6+ x [AlSiO 4 ] 6 (OH) x · n H 2 O have been studied by 23 Na MAS‐NMR and 1 H 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 1 H MAS‐NMR spectrum of the non‐basic phase Na 6 [AlSiO 4 ] 6 · 8H 2 O 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 1 H MAS‐NMR double peak spectrum of the basic hydro‐sodalite species Na 8 [AlSiO 4 ] 6 (OH) 2 · 4H 2 O 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 1 H MAS‐NMR spectrum of the hydroxy‐sodalite Na 8 [AlSiO 4 ] 6 (OH) 2 indicates substantial change in the chemical bond of the hydrogen atom upon dehydration of the tetrahydrate Na 8 [AlSiO 4 ] 6 (OH) 2 · 4H 2 O at 775 K. — The phases of the non‐basic hydro‐sodalites show 23 Na 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 23 Na 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.