Soft X-ray Absorption Spectroscopy Study of Spin Crossover Fe-Compounds: Persistent High Spin Configurations under Soft X-ray Irradiation

Abstract

Metal-organic complex exhibiting spin crossover (SCO) behavior has drawn attention for its functionality as a nanoscale spin switch. The spin states in the metal ions can be tuned by external stimuli such as temperature or light. This article demonstrates a soft X-ray–induced excited spin state trapping (SOXEISST) effect in Hofmann-like SCO coordination polymers of FeII(4-methylpyrimidine)2[Au(CN)2]2 and FeII(pyridine)2[Ni(CN)4]. A soft X-ray absorption spectroscopy (XAS) study on these polymers showed that the high spin configuration (HS; S = 2) was prevalent in Fe2+ ions during the measurement even at temperatures much lower than the critical temperatures (>170 K), manifesting HS trapping due to the X-ray irradiation. This is in strong contrast to the normal SCO behavior observed in FeII(1,10-phenanthroline)2(NCS)2, implying that the structure of the ligand chains in the polymers with relatively loose Fe-N coordination might allow a structural adaptation to stabilize the metastable HS state under the soft X-ray irradiation.

Thin Films of Nanocrystalline Fe(pz)[Pt(CN)4] Deposited by Resonant Matrix-Assisted Pulsed Laser Evaporation

“…Compared to the spectrum at 300 K, the spectrum recorded at 65 K is shifted to higher energies: 1.42 eV for L 3 and 0.38 eV for L 2 -edge maxima. According to results available in the literature, the observed transformation confirms the transition from the high spin to the low spin state [ 30 , 31 ], however, the results presented in Figure 5 a show an incomplete spin transformation. This observation is not consistent with the spin transformation results confirmed with Raman or UV-Vis measurements and we assign it to the soft X-ray-induced excited spin state trapping (SOXIESST) effect.…”

Cascade of Spin-State Transitions in the Intermetallic Marcasite FeP2

“…Two groups of absorption peaks at incident photon energies of 709 eV, 711.15 eV at the L 3 -edge and 722.4 eV, 724.35 eV at the L 2 -edge systematically evolve as a function of temperature, respectively. The exhibited distinct multipeak structures are characteristic for high-spin (HS) Fe 2+ for 300 K and low-spin (LS) Fe 2+ states for 15 K, − with a 3d 6 orbital occupancy of Fe which is justified by our DFT+DMFT calculations. For comparison, multiplet simulations are shown in Supplementary Figure S6, which confirm a LS to HS transition between 15 and 300 K.…”

Sublimable complexes with spin switching: chemical design, processing as thin films and integration in graphene-based devices

“…This effect could prevent a large fraction of the molecules from properly undergoing the thermal spin transition, as it has been previously observed in some bulk SCO materials and more recently for films of a SCO molecule, where the thermal spin transition was totally supressed. 36,61 Thus, since both films TF1 and TF2 show the typical SOXIESST effect up to 80 K and having a rather strong shifting to lower temperatures of their thermal spin transition, it could be reasonable to consider this high sensitivity to X-ray irradiation as a possible cause. A second additional explanation may arise from the very small size of nanoparticles in the film, not distinguishable in the AFM images collected (Fig.…”