Research article

Characterisation of temperature-dependent phase transitions in 2,2-trimethylenedioxy- 4,4,6,6-tetrachlorocyclotriphosphazene, N₃P₃Cl₄[O(CH₂)₃O]

Simon J Coles¹ , David B Davies² , Michael B Hursthouse¹ , Susanne L Huth¹ , Adem Kılıç³ , Mark E Light¹ , Marianne Odlyha² , John S Rutherford⁴ , Robert A Shaw² and Aylin Uslu³

¹School of Chemistry, University of Southampton, Highfield, Southampton. SO17 1BJ, UK

²School of Biological and Chemical Sciences, Birkbeck College (University of London), Malet Street, London WC1E 7HX, UK

³Department of Chemistry, Gebze Institute of Technology, Gebze, Turkey

⁴1 Barliath, Minard, Argyll PA32 8YQ, UK

author email corresponding author email

Chemistry Central Journal 2007, 1:20doi:10.1186/1752-153X-1-20

Published:	18 July 2007

Abstract

Background

The crystal structure of 2,2-trimethylenedioxy-4,4,6,6-tetrachlorocyclo triphosphazene has been determined at 120, 274 and 293 K. The result at 293 K confirms the room temperature Cmc2₁ structure, but at the lower temperatures the space group is Pna2₁. Nevertheless the basic structure remains the same, with only small displacements of the atoms, amounting to an average of 25 pm between 120 and 293 K.

Results

X-ray diffraction and DSC results indicate that the phase transition takes place in two steps between 274 – 293 K and provides an understanding of previous NQR results. In the intermediate temperature range the molecules are displaced from their room temperature positions in such a way as to give an average structure with Cmc2₁ symmetry.

Conclusion

The overall phase transition is consistent with the occurrence of a soft lattice mode at room temperature in which a large displacement of the molecule in the x-direction is coupled with a flexing motion about an axis defined by the nitrogen atoms in the N1 and N3 positions.