STRUCTURE ANALYSIS OF INTERCALATES

Pavla Capkova^1,2, Daniel Janeba1^1,2, Miroslava Trchová¹, Ludvík Beneš³, Klára Melanová³, Henk Schenk² and Jirí Votinský⁴

¹Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague 2, Czech Republic;
²Laboratory of Crystallogr.,University of Amsterdam, Nieuwe Achtergracgt 166, 1018WV Amsterdam, The Netherlands;
³Joint Laboratory of Solid State Chemistry, Academy of Sciences and University Pardubice, Studentská 84, 53009 Pardubice, Czech Republic,
⁴Department of Inorg. Chemistry, University Pardubice , Námistí Es. Legií 565, 53210 Pardubice

Keywords: intercalates, vanadyl phosphate, zirconium phosphate, molecular mechanics.

Intercalated layered structures usually exhibit a certain degree of disorder in position and orientation of guest molecules and disorder in stacking of layers. As a result of this disorder, it is not possible to prepare the single crystal of reasonable size for diffraction analysis. Powder diffraction diagrams are in addition affected by the strong preferred orientation of crystallites. Both effects (the disorder and the preferred orientation) make the diffraction analysis extremely difficult. The structure analysis of intercalates is usually focused to the following specific problems: the position and orientation of guest molecules, their ordering in the interlayer space and the stacking of layers. All these characteristics of structure - important for the porosity control in the interlayer space - are ruled by the nature of host-guest and guest-guest interactions. The deep understanding of structure-property relationship, which is necessary for the design of new intercalates with desirable properties, requires the complex structure analysis based on the combination of X-ray diffraction with the molecular mechanics simulation and vibrational spectroscopy.

Molecular mechanics simulations represent the powerful tool in structure analysis of difficult (partialy disordered structures). This method of structure determination is based on the energy minimization, using empirical force fields to describe the crystal energy. The complex structure analysis combines the informations obtained from X-ray diffraction and vibrational spectroscopy to create the strategy of modelling (molecular simulations). In spite of the limited information content of powder diffraction diagrams of intercalates, the comparison of these diagrams for host and intercalated sturucture is necessary for the building of initial model and for a preliminary estimation of structural changes due to the intercalation. The comparison of vibrational (IR and Raman) spectra for the host structure, intercalate and intercalating species provide us with the informations about the nature of host-guest interactions and about a possible distortions of host layers and guest molecules, due to the intercalation. All these informations are important for the strategy of modelling.

As a result of the complex structure analysis we get the complete description of the structure, including the description of a possible disorder and including the crystal energy and the individual components of the crystal energy. This way of structure analysis has been used in the investigation of phyllosilicates, intercalated with aluminium complex cations [1,2,3] ; montmorillonite intercalated with organoamonium cations [4], and vanadyl phospate [5] and zirconium phospate intercalated with ethanole [6]

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[3] D.J. Pruissen, P. Eapková, R.A.J. Driessen, H. Schenk,Applied CatalysisA165 (1997), 481
[4] D. Janeba, P. Capková, Z. Weiss, J.Mol.Model (1998) in print
[5] P. Capková, D. Janeba, L.Beneš, K. Melanová, H. Schenk, J.Mol.Model 4 (1998) in print
[6] P. Capková, L. Beneš, K. Melanová, H. Schenk, J Appl. Cryst., supplied 1997, in print