The Investigation of Spin-Crossover Systems by Raman Spectroscopy: A Review

Abstract

Spin-crossover (SCO) is a well-documented phenomenon, being intensely investigated by a respectable number of researchers during the last decades. The conventional method for the investigation of SCO properties is by performing magnetic susceptibility measurements. On the other hand, Raman has also been proposed as a promising characterization method since it is a non-bulk technique and allows, along with the monitoring of the SCO behavior, the parallel deep characterization of structure and molecular structure modifications, while it can also facilitate the determination of the entropy change related to the SCO event. There are several review articles focused on the analysis of the SCO phenomenon, the emerging applications of SCO materials and the importance of SCO/polymer composites, and elaborating on the vibrational effects on the investigation of SCO complexes; however, there has been no attempt to review solely the existing research efforts of the investigation of SCO phenomenon based on Raman spectroscopy. The main scope of this review is to focus on the main features, the challenges, and the key role of Raman spectroscopy in the investigation of 3d mononuclear complexes (comprising mainly of iron(II) complexes) and Hofmann-type metal organic frameworks (MOFs) exhibiting the SCO behavior. In addition, special focus is devoted to the research studies in which in situ Raman measurements are performed for the investigation of SCO systems. Finally, novelties, current challenges, future perspectives, and the contribution of Raman spectroscopy toward the practical application of SCO complexes are discussed.

Reversible Single-Crystal-to-Single-Crystal Transformations in a salEen Fe(III) Spin Crossover Sponge

“…Raman studies of 1 as a function of temperature were completed to provide further insight into the structural changes accompanying the HS to LS transition. It is expected that the force constant ( f ) of low-frequency vibrational modes associated with the Fe–O and of the Fe–N bonds, will be impacted by the spin state Figure a shows the heating cycle (phase 1) from low to high temperature (200 K to 360 K) of 1 .…”

Unique spin crossover pathways differentiated by scan rate in a new dinuclear Fe(ii) triple helicate: mechanistic deductions enabled by synchrotron radiation studies

“…Raman studies performed on 1 ·6H 2 O with a green laser (514 nm) and controlled cooling of 1 K min −1 revealed marker peaks of the HS and LS states, and increased laser power at 100 K resulted in spectral data consistent with the HS state (ESI,† Section S5). 58…”

Anomalous Pressure Response of Temperature-Induced Spin Transition and a Pressure-Induced Spin Transition in Two-Dimensional Hofmann Coordination Polymers

“…Raman spectroscopy is an effective means of characterizing ST phenomena because of the dramatic changes in structure and vibrational entropy accompanying ST. Variable-pressure Raman spectra of Isoq-Pt and Isoq-Pd compounds were acquired at room temperature using silicone oil and KBr as PTM. , In general, the testing of Raman spectroscopy under pressure using silicone oil as a PTM is adequate. However, to compare with the results of variable-pressure IR spectroscopy, variable-pressure Raman spectroscopy with KBr as PTM was also performed because silicone oil was not suitable as PTM for IR testing.…”