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Thomas Armbruster, J. Stolz, B. Hennessy

Site preference of exchanged alkylammonium ions in heulandite: single-crystal X-ray structure refinements

Single crystals (0.1-0.5 mm) of heulandite, Na_0.96K_0.09Ca_3.54[Al_8.62Si_27.51O₇₂] · n H₂O from Nasik, India, placed in a Teflon autoclave filled with a 2-4 M NaCl solution for 13 weeks at 423 K, yielded Na-exchanged heulandite. CH₃3NH⁺-, C₂H₅NH₃+-, n-C₃H₇NH₃⁺-, and (CH₃)₂NH₂⁺-exchanged heulandites were obtained by further treatment (four weeks at 423 K) with corresponding 1 M alkylammonium chloride solutions. Single-crystal X-ray structure refinements at 293 K of CH₃NH₃⁺-, n-C₃H₇NH₃⁺-, and (CH₃)₂NH₂⁺-exchanged heulandites performed in space group C2/m yielded R1 values of 3.45%, 4.05%, and 3.99%, respectively. Due to partial Si,Al ordering in the framework C₂H₅NH₃⁺-exchanged heulandite was triclinic, space group C-1(R1 = 3.64%). Seven to eight disordered and partly occupied alkylammonium ions per formula unit could be located in the structural channels, except for propylammonium of which for steric and kinetic reasons only traces were incorporated. Infrared powder-spectra and energy-dispersive analyses with a scanning electron microscope confirmed the incorporation of alkylammonium ions. The nitrogen positions of the CH₃NH₃-, C₂H₅NH₃-, and n-C₃H₇NH₃-molecules corresponded well with the nitrogen positions of NH₄⁺-exchanged heulandite refined by Yang and Armbruster (1998), while the (CH₃)₂NH₂-ions showed a different arrangement.

Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0044-2968
Volume: 215, 05/2000
Pages: 278

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