(Na4BH4)3+ guests inside aluminosilicate, gallosilicate and aluminogermanate sodalite host frameworks studied by 1H, 11B, and 23Na MAS NMR spectroscopy

We report tetrahydroborate aluminosilicate, gallosilicate and aluminogermanate sodalites studied by 11B, 1H and 23Na MAS NMR spectroscopy. The spectral parameters are consistent with the local environments of each investigated nucleus obtained from the crystal structures. The 11B MAS NMR spectra exhibit a sharp narrow line at about -49.0 ppm, which is assigned to BH4- enclathrated into the sodalite framework matrix. The lineshape of the signal shows no quadrupolar interactions due to discreteness and high symmetry of the BH4- unit as well as possible fast dynamic site exchange of hydrogen atoms. The 23Na MAS NMR signals also show a narrow Gaussian lineshape, which clearly indicates a single type of sodium coordination, and a centrosymmetrical charge distribution around the sodium atom. The 1H MAS NMR spectra can clearly distinguish between hydrogen in BH4- anions (-0.6 ppm), H3O2- anions (1.2 ppm) and H2O molecules (5.0 ppm). The structural properties of BH4- intercalation into sodalite framework matrix help connect the microporous materials to hydride-containing A, X and Y type zeolites.