Synthesis and crystal structure of gallosilicate- and aluminogermanate tetrahydroborate sodalites Na8[GaSiO4]6(BH4)2 and Na8[AlGeO4]6(BH4)2

Tetrahydroborate enclathrated sodalites with gallosilicate and aluminogermanate host framework were synthesized under mild hydrothermal conditions and characterized by X-ray powder diffraction and IR spectroscopy. Crystal structures were refined in the space group P-43n from X-ray powder data using the Rietveld method. Na8[GaSiO4]6(BH4)2: a=895.90(1) pm, V=0.71909(3)×10−6 nm3, RP=0.074, RB=0.022, Na8[AlGeO4]6(BH4)2: a=905.89(2) pm, V=0.74340(6)×10−6 nm3, RP=0.082, RB=0.026. The tetrahedral framework T-atoms are completely ordered in each case and the boron atoms are located at the centre of the sodalite cages. The hydrogen atoms of the enclathrated BH4- anions were refined on x, x, x positions, restraining them to boron–hydrogen distances of 116.8 pm as found in NaBD4.The IR-absorption spectra of the novel phases show the typical bands of the tetrahedral BH4- group as found in the spectrum of pure sodium boron hydride.The new sodalites are discussed as interesting BH4--containing model compounds which could release pure hydrogen.

Graphical abstractCoordination of the non-framework atoms in the gallosilicate tetrahydroborate sodalite together with three oxygen atoms of the framework around each sodium atom.Figure optionsDownload full-size imageDownload as PowerPoint slide