Premium
Sodium aluminogermanate hydroxosodalite hydrate Na 6+x [Al 6 Ge 6 O 24 ](OH) x · nH 2 O (x ≈ 1.6, n ≈ 3.0): Synthesis, phase transitions and dynamical disorder of the hydrogen dihydroxide anion, H 3 O 2 − , in the Cubic high‐temperature form
Author(s) -
Wiebcke Michael,
Sieger Peter,
Felsche Jürgen,
Engelhardt Günter,
Behrens Peter,
Schefer Jürg
Publication year - 1993
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.19936190728
Subject(s) - sodalite , crystallography , hydrate , chemistry , neutron diffraction , differential scanning calorimetry , x ray crystallography , raman spectroscopy , crystal structure , powder diffraction , analytical chemistry (journal) , diffraction , zeolite , physics , organic chemistry , thermodynamics , catalysis , biochemistry , chromatography , optics
Crystalline sodium aluminogermanate hydroxosodalite hydrate Na 6+x [Al 6 Ge 6 O 24 ](OH) x · nH 2 O with x ≈ 1.6 and n ≈ 3.0 has been synthesized by reacting Al 2 O 3 , GeO 2 and NaOH solution under hydrothermal conditions, and characterized by means of simultaneous thermal analysis, differential scanning calorimetry, X‐ray and neutron diffraction as well as 1 H and 23 Na MAS NMR and IR spectroscopy. The material undergoes a reversible structural phase transition at T c = 166 K (heating mode), which is actually a complex two‐step transformation as detected in DSC measurements. Structure refinements of the cubic high‐temperature form (cell constant a = 9.034(2) Å, room temperature) with single‐crystal X‐ray and powder neutron diffraction data have not yielded overall satisfactory results, probably due to the solid‐solution character of the hydrosodalite. The refinements nevertheless demonstrate that (i) the sodalite host framework is a strictly alternating array of corner‐linked AlO 4 and GeO 4 tetrahedra, and (ii) most polyhedral [4 6 6 8 ] cavities are occupied by four sodium cations and one orientationally disordered hydrogen dihydroxide anion, H 3 O 2 − , which possesses a strong central hydrogen bond. Variable‐temperature 1 H MAS NMR spectra unambiguously confirm the presence of H 3 O 2 − ions and, in addition, reveal a dynamical intraionic exchange between the central and terminal protons and a rotational diffusion of those anions to occur in the high‐temperature form. The nature of the guest complexes filling the remaining cages could not be unambiguously determined. Results are compared with those obtained in recent studies on the related sodium aluminosilicate hydrosodalite system of the general formula Na 6+x [Al 6 Si 6 O 24 ] (OH) x · nH 2 O.