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Rotational Polymorphism of Methyl-Substituted Ammonium Perchlorates

Published online by Cambridge University Press:  06 March 2019

M. Stammler ,
R. Bruenner ,
W. Schmidt  and
D. Orcutt
M. Stammler
Affiliation:
Aerojet-General Corporation, Sacramento, California
R. Bruenner
Affiliation:
Aerojet-General Corporation, Sacramento, California
W. Schmidt
Affiliation:
Aerojet-General Corporation, Sacramento, California
D. Orcutt
Affiliation:
Aerojet-General Corporation, Sacramento, California
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Abstract

The thermal transformations which take place in solid methyl-substituted ammonium perchlorates have been studied using high-temperature X-ray diffraction and differential thermal analysis techniques. In the temperature range from 20°C to their decomposition temperature (above 300°C), ammonium perchlorate and tetramethyl ammonium perchlorate undergo only one enantiomorphic phase transition, namely at 240 and 340°C (with decomposition), respectively. This I—II transition is ascribed to the beginning of the free rotation of the ClO4− ions. The rotation of the cations, however, begins below room temperature. If the symmetry of the cation is lowered by having both methyl groups and hydrogens arranged around the nitrogen (as in monomethyl, dimethyl, and trimethyl ammonium perchlorates), there is an additional enantiomorphic phase transition. This I—II transformation is ascribed to the rotation of the cations which have, in the partially substituted ions, two sets of non-equivalent symmetry axes (different moments of inertia). The temperatures of transformation are discussed in terms of the space requirements for rotation. Symmetries and cell dimensions of some modifications were determined.

Type
Research Article
Information
Advances in X-Ray Analysis , Volume 9: Fourteenth Annual Conference on Applications of X-ray Analysis, August 25-27, 1965 , 1965 , pp. 170 - 189
Copyright
Copyright © International Centre for Diffraction Data 1965

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