Related Experiment Video
Updated: Jan 9, 2026

Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals
Published on: April 14, 2020
Tracking the HS-HS, HS-LS, and LS-LS States in the Spin Transition of a Dinuclear Fe(II) Complex by Broadband FTIR
Marcel Walter1, Eike F Kuhlemann2, Tarek Al Said3
1Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
Abstract:
Highly resolved vibrational spectra of the mononuclear Fe(II) spin-crossover complex [Fe(bpz)2(bipy)]; (bpz = dihydrobis(pyrazolyl)borate) and its dinuclear counterpart [{Fe(bpz)2}2μ-(ac(bipy)2)] (ac(bipy)2 = bridging ligand) are obtained by temperature-dependent far-infrared (FIR) spectroscopic measurements and assigned with the help of density functional theory (DFT) calculations. The experimental data confirm the high-spin (HS) state of the complexes at high temperature (≈ 200 K) and the low-spin (LS) state at 5 K. In the dimer, enhancement of otherwise absent vibrational modes at 335 cm-1 and 504 cm-1 around T1/2 reflects the presence of a mixed-spin HS-LS state during the course of the spin transition between HS-HS and LS-LS. The metastable HS state of the dinuclear complex resulting from light irradiation (532 nm) at 10 K results from a direct spin-state transition from LS-LS to HS-HS.
Related Concept Videos
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)
Valence Bond Theory
UV–Vis Spectroscopy: Molecular Electronic Transitions
NMR Spectroscopy: Spin–Spin Coupling

