(Na_4BH_4)~(3+) guests inside aluminosilicate, gallosilicate and aluminogermanate sodalite host frameworks studied by ~1H, ~(11)B, and ~(23)Na MAS NMR spectroscopy

摘要

We report tetrahydroborate aluminosilicate, gallosilicate and aluminogermanate sodalites studied by ~(11)B, ~1H and ~(23)Na MAS NMR spectroscopy. The spectral parameters are consistent with the local environments of each investigated nucleus obtained from the crystal structures. The "B MAS NMR spectra exhibit a sharp narrow line at about -49.0 ppm, which is assigned to BH_4~- enclathrated into the sodalite framework matrix. The lineshape of the signal shows no quadrupolar interactions due to discreteness and high symmetry of the BH_4~- unit as well as possible fast dynamic site exchange of hydrogen atoms. The ~(23)Na 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 BH_4~- anions ( -0.6 ppm), H_3O_2~- anions (1.2 ppm) and H_2O molecules (5.0 ppm). The structural properties of BH_4~-intercalation into sodalite framework matrix help connect the microporous materials to hydride-containing A, X and Y type zeolites.