Toward an iron(II) spin-crossover grafted phosphazene polymer

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Cyclotriphosphazene ligands offer versatile platforms for designing functional materials.
• 2,2':6',2″-terpyridine (Terpy) moieties are known to form stable metal complexes.
• Spin crossover (SCO) materials exhibit tunable magnetic properties with potential applications in sensors and data storage.

Purpose of the Study:

• To synthesize novel cyclotriphosphazene ligands incorporating terpyridine units.
• To prepare and characterize iron(II) complexes with these ligands.
• To investigate the spin crossover properties of the resulting complexes and polymeric analogues.

Main Methods:

• Ligand synthesis and characterization.
• Formation and spectroscopic analysis (UV-Vis, resonance Raman, Mössbauer) of iron(II) complexes.
• Variable-temperature magnetic susceptibility measurements.
• Density functional theory (DFT) calculations.

Main Results:

• Two new cyclotriphosphazene ligands (L(1), L(2)) and their polymeric forms (L(1P), L(2P)) were successfully synthesized.
• Iron(II) complexes with an Fe(II)Terpy(2) core were formed.
• Spin crossover behavior was observed, with extended spacer lengths in L(2) and L(2P) inducing SCO at higher temperatures.
• Polymeric analogues exhibited similar behavior to their monomeric counterparts.

Conclusions:

• The synthesized ligands and their iron(II) complexes demonstrate tunable spin crossover properties.
• Extending ligand spacer length is an effective strategy for achieving high-temperature SCO.
• These findings provide a route towards developing malleable spin crossover materials.