Spin state switching of metal complexes by visible light or hard X-rays

Abstract

Electromagnetic stimuli of spin crossover compounds restricted to UV-vis light irradiation for many years could be recently extended to X-ray excitation. This review covers a large variety of light-induced effects, as well as recent analogues stimulated by X-ray irradiation which have not yet been reviewed. The focus is also on multistable multinuclear spin crossover compounds which are the subject of lively discussions within the spin crossover community. Their spin transition often occurs incompletely and with different switching mechanisms. In this review, we recall a predicted sequential switching induced thermally as well as a concerted stimulation mechanism by light irradiation for these interesting multifunctional materials.

Switching Magnetic Properties by a Mechanical Motion

“…This effect has an entropic origin due to a higher number of microstate and vibrational entropy in the HS configuration [5]. Light can also be used at a low temperature to trigger a spin transition from LS to HS by a light induced excited spin state trapping (LIESST) effect ( Figure 1a) [22,23]. In this case, an increase of the magnetization is observed upon irradiation at low temperature, indicating the population of the metastable HS state.…”

Direct Evidence of a Photoinduced Electron Transfer in Diluted “Molybdenum‐Copper” Molecular Compounds

“…Molybdenum‐copper complexes have attracted great attention over the past decade due to the interesting photomagnetic phenomena that have been reported for these systems . Most of the compounds display a reversible photoinduced magnetic bistability that has been developed into various forms: three‐dimensional networks, molecular complexes, high nuclearity clusters,, chains,, nanoparticles, and films .…”

“…Molybdenum-copper complexes have attracted great attention over the past decade due to the interesting photomagnetic phenomena that have been reported for these systems. [1][2][3][4][5][6][7][8][9][10] Most of the compounds display a reversible photoinduced magnetic bistability that has been developed into various forms: three-dimensional networks, [11][12][13] molecular complexes, [14][15][16][17][18] high nuclearity clusters, [19,20] chains, [21,22] nanoparticles [23,24] and films. [25][26][27] In addition, the integration of Mo-Cu complexes viewed as magnetic switches into sophisticated architectures [28,29] has been performed with success as well as their transformation into promising materials with various properties.…”

Spin crossover in the Prussian blue analogue FePt(CN)6induced by pressure or X-ray irradiation

“…Reversible SCO induced by radiation (light, soft and hard X-rays) have been previously observed but at low temperature, where radiation exposure causes an excitation to the HS state. [50][51][52][53] Irreversible spin changes induced by radiation are less documented, but could involve local structural and/or chemical changes in addition to the spin transition. 50,54 In our case, measurements upon decompression would help ascertain the reversibility of the spin change observed from radiation.…”