Related Experiment Video
Updated: Mar 30, 2026
High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Vibration-reorientation dynamics, structural changes and its interrelation with the phase transition in
Natalia Górska1, Edward Mikuli1, Maria Łabanowska1
1Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
Abstract:
Polycrystalline hexakis(urea-O)chromium(III) tetrafluoroborate possesses in the temperature range of 295-105 K one solid-solid phase transition at T(C) ≈ 255 K. Analysis of the band shapes associated with the ν(as)(CN) and δ(as)(NH2) vibrational modes of the Fourier transform infrared absorption (FT-IR) spectra, registered in the temperature range of 295-10 K, indicated existence of fast (τ(R) ≈ 10(-12) s) reorientational motion of the protons from NH2 groups belonging to OC(NH2)2 (urea) ligands, which does not suddenly change at T(C). Moreover, splitting of the IR bands associated with the ν(as)(NH), ν(s)(NH) and ν(as)(BF)F2/ν(s)(CN) modes at T(C) indicated that this phase transition is associated with a change of crystal structure. Similar analysis of the Raman scattering bands (FT-RS), associated with the δ(s)(FBF)E, ν(s)(BF)A and ν(as)(BF)F2/ν(s)(CN) vibrational modes, indicated fast reorientation of the BF4(−) ions, which does not suddenly change at T(C), and additionally confirmed structural character of this phase transition. Results obtained from vibrational spectroscopy measurements are compatible with that obtained by electron paramagnetic resonance spectroscopy (EPR) measurements in function of temperature, where rapid narrowing of the EPR line in the vicinity of the T(C) was observed.
Related Concept Videos
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:22Structures of Solids
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
01:24IR Spectroscopy: Molecular Vibration Overview
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
02:18X-ray Crystallography
Diffraction
Diffraction is the change in the direction of travel experienced by an electromagnetic wave when it encounters a physical barrier whose dimensions are comparable to those of the wavelength of the light. X-rays are electromagnetic radiation with wavelengths about as long as the distance between neighboring...