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 Rielveld method. Na-8[GaSiO4](6)(BH4)(2): a = 895.90(1) pm, V = 0.71909(3) x 10(-6) nm(3), R-P = 0.074: R-B = 0.022, Na-8[AlGeO4](6)(BH4)(2): a = 905.89(2) pm, V = 0.74340(6) x 10(-6) nm(3), R-P = 0.082, R-B = 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 116.8pm 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. (c) 2006 Elsevier Inc. All rights reserved.