Pressure-Induced Mixed States Caused by Spin-Elastic Interactions during First-Order Spin Phase Transition in Spin Crossover Compounds

Abstract

Recently, the possibility of exploiting the phenomenon of spin transition (ST) has been intensively investigated; therefore, it is particularly important to study the behavior of ST under various stimuli. Here, the shape and content of the intermediate phase of ST in Hoffmann-like compounds [Fe(Fpz) 2 M(CN) 4 ] (M = Pt, Pd) under external stimuli are studied. For this purpose, magnetic and Raman spectroscopy studies were carried out. In pressure-induced spin transition (PIST), a mixture of high-spin and low-spin states appears, while in temperature-induced spin transition (TIST), a homogeneous state occurs. The first-order ST induced by pressure has a hysteresis but is not abrupt. However, the temperature-induced spin transition at ambient pressure is hysteretic and abrupt. To investigate this difference, we discuss using a thermodynamic model that considers elastic interactions, showing that the slope of the hysteresis loop is related to the appearance of internal pressure, which is related to the difference in sample compressibility under high-spin and low-spin states.

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

“…The value of P 1/2 Pt is less than that of P 1/2 Pd , a fact that is consistent with the order of ligand field strength reported in ref . The pressure interval difference between the ST of the two compounds, Δ P (Pd) > Δ P (Pt), is similar to the results described in ref , which may be related to the different mechanical properties of the compounds …”

“…Isoq-Pt shows a more sudden ST behavior than Isoq-Pd because the mechanical properties of Isoq-Pt change more significantly than Isoq-Pd before and after ST, which are conducive to the generation of spin domains. 52 In the variable-pressure Raman and IR spectra using KBr as a PTM, both Isoq-Pt and Isoq-Pd experienced "gradual" PIST under pressure, where the PIST behavior of Isoq-Pt changed particularly significantly, and the pressure interval of its ST was even larger than that of Isoq-Pd. Interestingly, in the X-ray diffraction experiment using microcrystalline powder, we found that both Isoq-Pt and Isoq-Pd showed the same PIST behavior as the single crystal.…”

“…Under variable-pressure powder X-ray diffraction, Raman, and UV–vis absorption spectroscopy at room temperature using silicone oil as PTM, we found that Isoq-Pt undergoes an “abrupt” PIST under pressure, whereas Isoq-Pd undergoes a “gradual” PIST under pressure. Isoq-Pt shows a more sudden ST behavior than Isoq-Pd because the mechanical properties of Isoq-Pt change more significantly than Isoq-Pd before and after ST, which are conducive to the generation of spin domains . In the variable-pressure Raman and IR spectra using KBr as a PTM, both Isoq-Pt and Isoq-Pd experienced “gradual” PIST under pressure, where the PIST behavior of Isoq-Pt changed particularly significantly, and the pressure interval of its ST was even larger than that of Isoq-Pd .…”

“…The pressure interval difference between the ST of the two compounds, ΔP(Pd) > ΔP(Pt), is similar to the results described in ref 36, which may be related to the different mechanical properties of the compounds. 52 Variable-pressure Raman spectroscopy measurements of Isoq-Pt and Isoq-Pd microcrystalline powders using KBr as the PTM are shown in Figures S3 and S4. The pressure dependence of γ HS displayed in Figures S3d and S4d shows that both compounds exhibit a more "gradual" PIST behavior compared with that derived from using silicone oil as PTM.…”

Spin-state dependent pressure responsiveness of Fe(ii)-based triazolate metal–organic frameworks

“…10 Importantly, both factors also influence the critical pressure where pressure-induced amorphisation occurs. 23 There has been interest in the pressure-dependent spin-state of MOF-related Hoffman-type clathrates [24][25][26] and the elastic properties of molecular Fe(II) SCO complexes, 27,28 highlighting that changing the spin-state significantly impacts B. The impact of the spin-state of metal centres within the metal-node on the mechanical properties of MOFs has not been explored to our knowledge.…”