Rotational dynamics of the imidazolium ion in cyanide-bridged dielectric framework materials. Issue 79 (4th September 2020)

• Record Type: Journal Article
• Authors: Phillips, Anthony E.; Cai, Guanqun; Demmel, Franz
• Is Part Of: Chemical communications. Volume 56:Issue 79(2020)
• Page Start: 11791
• Page End: 11794
• Publication Date: 2020-09-04
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1039/d0cc05238h
• Languages: English
• ISSNs: 1359-7345

Abstract

Abstract : Quasielastic neutron scattering reveals the geometry and timescale of the dielectric switching dynamics in a series of elpasolite-like framework materials. Abstract : Reorientation of organic cations in the cubic interstices of cyanoelpasolite molecular perovskites results in a variety of structural phase transitions, but far less is known about these cations' dynamics. We report quasielastic neutron scattering from the materials (C3 H5 N2 )2 K[M III (CN)6 ], M = Fe, Co, which is directly sensitive to the rotation of the imidazolium ion. The motion is well described by a circular three-site hopping model, with the ion rotating within its plane in the intermediate-temperature phase, but tilting permanently in the high-temperature phase. Thus the two rhombohedral phases, which are crystallographically rather similar, have markedly different dynamics. The activation energy of rotation is about 10 kJ mol −1 and the barrier between orientations is 6 kJ mol −1 . Our results explain two anomalous features in these materials' dielectric constants.