A Known Iron(II) Complex in Different Nanosized Particles: Variable-Temperature Raman Study of Its Spin-Crossover...

Area of Science:

• Coordination Chemistry
• Materials Science
• Solid-State Physics

Background:

• Spin-crossover (SCO) complexes exhibit temperature-dependent spin state changes, crucial for molecular switches and sensors.
• The SCO behavior of [Fe^II{N(CN)₂}₂(abpt)₂] (complex 1) is known, with polymorph B featuring two distinct Fe sites.
• Previous studies established high-spin (HS) states at room temperature and a high-spin to low-spin (LS-HS) transition upon cooling.

Purpose of the Study:

• To synthesize and characterize SCO complex 1 in three distinct particle sizes (∼300 nm, ∼80 nm, ∼20 nm).
• To investigate the influence of particle size on the spin-crossover properties of complex 1.
• To utilize variable-temperature Raman spectroscopy to probe SCO behavior and validate findings with magnetic susceptibility data.

Main Methods:

• Synthesis of complex 1 in three particle size fractions.
• Characterization using elemental analysis, ATR, UV/vis spectroscopy, powder X-ray diffraction, and scanning electron microscopy (SEM).
• Variable-temperature Raman spectroscopy (300-80 K) focusing on spin-sensitive vibrational modes (ν(Fe-N), δ(NFeN), ν(C≡N)).

Main Results:

• Successful preparation of complex 1 in average particle sizes of ∼300, ∼80, and ∼20 nm.
• Raman studies confirmed the HS-HS to LS-HS transition, with new peaks appearing in the LS state.
• Smaller particle sizes exhibited the LS-HS transition at higher temperatures, with a T_1/2 shift up to ∼30 K for the 20 nm sample compared to the 300 nm sample.

Conclusions:

• Particle size significantly influences the SCO transition temperature of complex 1, with smaller particles stabilizing the high-spin state at higher temperatures.
• Variable-temperature Raman spectroscopy is a valuable tool for studying SCO phenomena and complements magnetic susceptibility measurements.
• The observed particle size effect on SCO properties highlights potential for nanoscale SCO materials with tunable transition temperatures.