NMR study of ferroelastic phase transition of tetramethylammonium tetrabromocobaltate

作者：Lim Ae Ran^*; Kim Sun Ha

来源：Journal of Molecular Structure, 2016, 1119: 479-483.

DOI：10.1016/j.molstruc.2016.04.089

• [N(CH3)(4)](2)CoBr4
• Crystal structure
• Nuclear magnetic resonance
• Phase transition
• Ferroelastics

Static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments were carried out on H-1, C-13, and N-14 nuclei in order to understand the structural changes of the N(CH3)(4) groups in [N(CH3)(4)](2)CoBr4 near the ferroelastic phase transition temperature T-C. The two chemically inequivalent N(CH3)(4) groups were distinguished using C-13 cross-polarization/(CP)MAS and N-14 static NMR. The changes in chemical shifts, line intensities, and the spin-lattice relaxation time near T-C can be correlated with the changing structural geometry, which underlies the phase transition. The N-14 NMR spectra indicated a crystal symmetry change at T-C, which is related to the ferroelastic domain with different orientations of the N(CH3)(4) groups. The ferroelastic domain walls were confirmed by optical polarizing microscopy, and the wall orientations were described by the Sapriel theory. The transition to the ferroelastic phase was found to be related to the orientational ordering of the N(CH3)(4) groups.

• 出版日期2016-9-5