ISSN:
0044-2313
Keywords:
Sodium aluminogermanate
;
sodalite
;
hydrogen dihydroxide anion
;
crystal structure
;
phase transition
;
dynamical proton exchange
;
MAS NMR
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
Natriumalumogermanat-Hydroxosodalithhydrat Na6+x[Al6Ge6O24](OH)x · nH2O (x ≈ 1,6, n ≈ 3,0): Synthese, Phasenumwandlungen und dynamische Fehlordnung des Hydrogendihydroxid-Anions,H3O2-,in der kubischen HochtemperaturformKristallines Natriumalumogermanat-Hydroxosodalithhydrat Na6+x[Al6Ge6O24](OH)x · nH2O mit x ≈ 1,6 und n ≈ 3,0 wurde durch Reaktion von Al2O3, GeO2 und NaOH-Lösung unter hydrothermalen Bedingungen hergestellt und mit Hilfe der Simultanthermoanalyse, Dynamischen Differenz-Kalorimetrie (DSC), Röntgen- und Neutronenbeugung sowie 1H- und 23Na-MAS-NMR- und IR-Spektroskopie charakterisiert. Die Verbindung durchläuft eine reversible strukturelle Phasenumwandlung bei Tc = 166 K (Heizmodus), die tatsächlich, wie in DSC-Messungen festgestellt wurde, als komplexe Zweistufentransformation abläuft. Struktur-
Notes:
Crystalline sodium aluminogermanate hydroxosodalite hydrate Na6+x[Al6Ge6O24](OH)x · nH2O with x ≈ 1.6 and n ≈ 3.0 has been synthesized by reacting Al2O3, GeO2 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 1H and 23Na MAS NMR and IR spectroscopy. The material undergoes a reversible structural phase transition at Tc = 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 AlO4 and GeO4 tetrahedra, and (ii) most polyhedral [4668] cavities are occupied by four sodium cations and one orientationally disordered hydrogen dihydroxide anion, H3O2-, which possesses a strong central hydrogen bond. Variable-temperature 1H MAS NMR spectra unambiguously confirm the presence of H3O2- 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 Na6+x[Al6Si6O24] (OH)x · nH2O.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/zaac.19936190728
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