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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 6 Issue 2 (2001) pp 73-77

A Pedagogical Illustration of the Determination of the Nature and Strength of Bonds in Crystalline Compounds from X-ray Diffraction and Infrared Spectroscopy Studies

Pierre Couchot,† Sandrine Monney,*,† George D. Sturgeon,‡ and Michael Knorr†

†Département de Chimie, Université de Franche Comté, 25030 Besançon Cedex, France, ‡Department of Chemistry University of Nebraska, Lincoln, Nebraska 68588
Received June 29, 2000. Accepted October 17, 2000

Published online: 9 March 2001

Abstract. This article describes a method used to teach students how X-ray crystallography and infrared spectroscopy analysis can be used to obtain information about the nature and strength of the bonding in the crystalline compounds MIMIII(SO4)2 (with MI = K+, Rb+, Cs+ and MIII = Al3+, Cr3+, Fe3+). These sulfates form an isomorphic series. The influences of specific MI and MIII ions on the variation of the a and c parameters and on the position of IR absorption bands are described. Additionally, X-ray crystallography and infrared spectroscopy studies of the double sulfates MIMIII(SO4)2 show students the existence of [SO4–MIII–SO4]– layers in the crystallized products; the covalent character of MIII–O attractions, which give cohesion in these layers; the existence of MI layers between [SO4–MIII–SO4]– layers, and the electrovalent character of MI–O interactions.

Key Words:  In the Classroom; physical chemistry; X-ray; crystallography; crystals

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Issue date: April 6, 2001

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