Volume 92, Issue 2 pp. 168-176
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Polymorphism in Dialkylammonium Chlorides. An Adiabatic Calorimetry Study

Michiel J. M. van Oort

Michiel J. M. van Oort

Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3

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Mary Anne White

Mary Anne White

Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3

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First published: Februar 1988
Citations: 18

Abstract

The heat capacities of four di-n-alkylammonium chlorides (di-n-pentylammonium chloride, di-n-hexylammonium chloride, di-n-octylammonium chloride, and di-n-decylammonium chloride) were measured from T = 25 K to 350 K using adiabatic calorimetry. All of the compounds investigated were observed to undergo solid-solid phase transitions in the temperature region examined. The thermodynamic properties obtained for these compounds were compared with those of the layered perovskites (alkylammonium metal halides) and the mono-n-alkylammonium chlorides. The high entropies of the solid-solid phase transitions suggest that there is a significant amount of conformational disorder in the high-temperature phase, most likely due to solid-state alkyl-chain melting, analogous to the layered perovskites and the monoalkylammonium chlorides. The contribution of a CH2 unit to the heat capacity of these complexes was calculated and compared to the n-alkanes and the layered perovskites.

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