23Na MAS-NMR and1H MAS-NMR Studies in the Hydro-Sodalite System

Gallium substitution in the alumosilicate framework: synthesis and structural studies of hydro sodalites

A series of hydro sodalites of composition Na6[Al1−yGaySiO4]6(H2O)8(0 ≤y≤ 1) have been prepared from Na6+x[Al1−yGaySiO4]6(OH · H2O)x(H2O)8−4xsodalites by NaOH/H2O exchange methods carried out in acidic aqueous media. One of the end members (y= 1) Na6[GaSiO4]6(H2O)8is obtained from Na8[GaSiO4]6I2by a hydrothermal transformation process. The polycrystalline samples are characterized by Rietveld refinements using X-ray powder diffraction data. The cell parameter fluctuates slightly from the [AlSiO4]6to the [GaSiO4]6framework with an average value of 884.8 pm. The occurrence of an almost constant cell parameter has been explained as a combined effect of hydrogen bonding between the oxygen atoms of the entrapped water (or the occluded [Na3□(H2O)4]3+complex in theβ-cage as a whole), and the framework together with six-ring window deformation. During XRD refinements both aluminium and gallium atoms have been converged to a single crystallographic site. The Al/Ga—O bond distance therefore indicates the mean of Al—O and Ga—O distances, which increases with increasing gallium content in the framework. However, the Si—O distance remains almost constant at 162.9 pm at any Ga/Al ratio. The coupled twisting of the (Al,Ga)O4and SiO4tetrahedra confirms the increase of tilt angles and decrease of six-ring pore dimension upon aluminium replacement by gallium in the framework. Results of1H and29Si MAS NMR as well as FTIR spectroscopy are also discussed in terms of successive gallium incorporation in the alumosilicate hydro sodalite frameworks.

Influence of sodium ion dynamics on the 23Na quadrupolar interaction in sodalite: a high-temperature 23Na MAS NMR study

High-temperature 33Na MAS NMR experiments up to 873 K for a number of different sodalites (Na8[AlSiO4]6(NO3)2, Na8[AlSiO4]6(NO2)2, Na8[AlSiO4]6I2, Na7.9[AlSiO4]6(SCN)7.9 x 0.5H2O, Na8[AlGeO4]6(NO3)2, and Na7[AlSiO4]6(H3O2) x 4H2O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite beta-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.