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N-methyl-N-alkylpyrrolidinium hexafluorophosphate salts : novel molten salts and plastic crystal phases

journal contribution
posted on 01.02.2001, 00:00 authored by J Goldingm, N Hamid, D MacFarlane, Maria ForsythMaria Forsyth, C Forsyth, C Collins, J Huang
A new series of salts, based on the N-methyl-N-alkylpyrrolidinium cation and the PF6- anion, are reported and their thermal properties described for alkyl = Me, Et, Pr, Bu, Hx, and Hp. X-ray structures of several of the salts are also reported. The N,N-dimethylpyrrolidinium hexafluorophosphate has a melting point greater than 390 °C; however, the N-methyl-N-butylpyrrolidinium derivative melts at 70 °C. Most of the PF6- salts were observed to have lower melting points in comparison with the analogous iodide salts. Most of the salts exhibit one or more thermal transitions prior to melting and a final entropy of melting less than 20 J K-1 mol-1, behavior which has previously been associated with the formation of plastic crystal phases. Good crystal structure solutions were obtained at low temperatures in the case of the alkyl = propyl and heptyl derivatives. The loss of diffraction peaks and changes in symmetry at higher temperatures indicated the presence of dynamic rotational disorder, supporting the understanding that the plastic properties arise from rotational motions in the crystal.

History

Journal

Chemistry of materials

Volume

13

Issue

2

Pagination

558 - 564

Publisher

American Chemical Society

Location

Washington, D.C.

ISSN

0897-4756

eISSN

1520-5002

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2001, American Chemical Society