Experimental and Theoretical Studies of Hybrid (C3N2H5)2SbF5 Crystal With the Phase Transition

Abstract

An organic–inorganic compound (C₃N₂H₅)₂SbF₅ — bis(imidazolium)pentafluoroantimanate — was investigated. This crystal undergoes a structural phase transition. The phase transition was studied with the use of the infrared spectra of powdered crystal suspended  in  Nujol  and  Fluorolube oil  in  a  wide range of internal vibration   of   the  (C₃N₂H₅)₂⁺  and  SbF₅^2- ions  (i.e.,  from   4000  to 400 cm^-1) in the  temperature  range  from 183 K  (154 K in Fluorolube)  to 300 K. The room temperature infrared spectrum in KBr and the Raman spectrum were achieved. The infrared measurement results showed a phase transition at 223 K (upon cooling). Temperature-depended changes of wavenumber, half-width, a center of gravity, and bands intensity were analysed in order to describe the contribution of cationic and anionic dynamics to the phase-transition mechanisms. Density functional theory formalism was applied to theoretical studies of normal vibration wavenumbers. For the optimized structure, harmonic frequencies and infrared intensities with Raman activities were calculated by the hybrid tree-parameter density functional model. Hydrogen bonds for the theoretical moiety were found. The results were compared with the experimental data. Electrostatic charges for the investigated molecules were calculated using the natural bond orbital method and Mulliken methods.