%0 Journal Article
%A Gatta, G. D.
%A Nestola, F.
%A Bromiley, G. D.
%A Mattauch, S.
%T The real topological configuration of the extra-framework content in alkali-poor beryl: a multi methodological study
%J American mineralogist
%V 91
%@ 1945-3027
%C Washington, DC
%I Soc.
%M PreJuSER-57967
%P 29 - 34
%D 2006
%Z Record converted from VDB: 12.11.2012
%X The crystal structure of alkali/water-poor beryl (1120 + Na2O + Cs2O < 1.2 wt%) was reinvestigated by means of laser ablation inductively coupled plasma mass spectroscopy, thermogravimetric analysis, neutron diffraction, and polarized infrared spectroscopy to determine the real topological configuration of the extra-framework content in the six-membered ring channels. Analysis of the nuclear density Fourier map suggests that the (water) oxygen is located along the sixfold axis at the 2a site (0,0, 1/4), whereas the (water) protons are at -0.028(7), -0.071(3), 0.332(1). The hydrogen atoms are distributed in 6 x 2 equivalent positions, above and below the oxygen site. Geometrical configuration of the water molecule is well defined: the O-H bond distance is 0.949(18) angstrom and the H-O-H bond angle is 106.9(2.2)degrees. The (HH)-H-... vector is oriented at similar to 4 degrees from [001]. This configuration is completely different from that found in alkali-rich beryl, where the (HH)-H-... vector is perpendicular to [00 1]. Na is probably located, with the H2O oxygen, at the 2a site. According to the chemical analysis, which shows that the amounts of other alkali and earth-alkali cations are negligible (Rb, K, Mg, Mn <= 110 ppm, Ca <= 225 ppm, Cs <= 430 ppm), no effect of other cations on the extra-framework population was observed in the structural refinement. The final agreement index (R-1) of the structural refinement was 0.037 for 34 refined parameters and 160 unique reflections with F-0 > 4 sigma(F-0). The topological configuration of the H2O molecule into the channel is confirmed by the spectroscopic investigation. Polarized single-crystal IR spectra show that the H2O molecule is oriented with the molecular symmetry axis perpendicular to the hexagonal axis and (HH)-H-... vector parallel (or quasi-parallel) to [001].
%K J (WoSType)
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000234527900004
%R 10.2138/am.2006.1896
%U https://juser.fz-juelich.de/record/57967