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 image 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 image group as found in the spectrum of pure sodium boron hydride. The new sodalites are discussed as interesting image-containing model compounds which could release pure hydrogen.