Monitoring of Fe(II) Spin Transition in Cu(II)-Doped Spin-Crossover Nanoparticles

Experimental protocols based on Electron Paramagnetic Resonance (EPR) and Raman spectroscopy are presented for the investigation of the Fe(II) spin transition in Cu(II)-doped 1-D spin-crossover (SCO) nanoparticles of the type [Fe_1-xCu_x(NH₂trz)₃]Br₂ where x = 0.03 and 0.06 and NH₂trz = 4-amino-1, 2, 4-triazole. The resulting nanoparticles were characterized using Transmission Electron Microscopy (TEM), Infrared (IR) spectroscopy, and powder X-ray diffraction (p-XRD). Magnetic susceptibility measurements revealed a dependence on the scan rate, with critical temperatures and hysteresis widths varying accordingly. EPR spectroscopy provided insights into the doped nanoparticles' structural changes and spin-state transitions. The Cu(II) dopants exhibited significant g-factor anisotropy and hyperfine structure, indicative of a distorted octahedral coordination. The EPR spectra indicated that the spin transition occurs in domains populated by ions of the same spin state. Cu(II) ions show different spectral characteristics depending on whether they are in high-spin or low-spin domains of Fe(II). Changes in Raman bands induced by laser power reveal structural and electronic rearrangements during the LS to HS transition. The findings provide insights into metal-ligand interactions and the molecular mechanisms underlying the SCO process.