Peters, L., Knorr, K., Evans, J. S. O., Senyshyn, A., Rahmoun, N. S. and Depmeier, W. (2007) Proton positions in and thermal behaviour of the phase 4 CaO center dot 3 Al2O3 center dot 3 H2O and its thermal decomposition to vertical bar(OCa4)(2)vertical bar Al12O24 -SOD, determined by neutron/X-ray powder diffraction and IR spectroscopic investigations. Zeitschrift Fur Kristallographie, 222 (7). pp. 365-375. DOI 10.1524/zkri.2007.222.7.365.

Abstract

The proton positions in the phase 4 CaO center dot 3 Al2O3 center dot 3 H2O (C(4)A(3)H(3)) were determined by neutron diffraction experiments at room temperature and 5 K. Two crystallographically distinct proton sites, 16g and 8f in space group Abma, were located from the evaluation of difference Fourier maps. Additionally, IR spectroscopic measurements were carried out to further characterise the observed OH groups. On the basis of this knowledge and due to topological considerations, we propose to write C4A3H3 according to the IUPAC nomenclature for microporous materials as an interrupted framework host structure with the formula vertical bar Ca-8(OH)(4)vertical bar(2) [(Al4Al8[4][1;3])-Al-[4][1;4]center dot O-20([2])(OH)(8)([1])](2h){3; 4-ring}(p){0[4(6)6(8)]) (Abma) - -SOD. X-ray diffraction experiments in the temperature range from 28 K to 973 K give an insight into the thermal behaviour of the phase C(4)A(3)H(3), and its topotactic condensation to vertical bar Ca8O2 vertical bar[(Al12O24[2])-O-[4][1;4]](h){3; 4-ring}(p)center dot{0[4(6)6(8)]}(I (4) over bar 3m)-SOD (C(4)A(3)) + 6 H2O. The questioned fractional coordinates of the framework oxygens in the decomposition product C(4)A(3), as described in the first structure determination, were corrected by a structure refinement using the Rietveld method. It is shown unambiguously that vertical bar(OCa4)(2)vertical bar center dot[Al12O24]-SOD has a sodalite-type structure.

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