Supramolecular spin-crossover iron complexes based on imidazole-imidazolate hydrogen bonds

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Tripodal ligands offer unique coordination environments for metal ions.
• Spin crossover (SCO) in iron complexes is crucial for developing switchable materials.
• Understanding mixed-valence iron systems is key to designing advanced functional materials.

Purpose of the Study:

• To synthesize and characterize novel iron complexes using a tripodal ligand.
• To investigate the spin crossover properties of Fe(II) and Fe(III) complexes.
• To explore the structural and electronic behavior of mixed-valence iron compounds.

Main Methods:

• Synthesis of iron complexes with a tris[[2-[(imidazole-4-yl)methylidene]amino]ethyl]amine ligand.
• Single-crystal X-ray structure determination for all synthesized complexes.
• Magnetic susceptibility and Mössbauer spectroscopy to study spin states and electronic transitions.

Main Results:

• Five novel iron complexes were synthesized and characterized, including Fe(II), Fe(III), and mixed-valence Fe(II)-Fe(III) species.
• Most complexes exhibited spin crossover behavior, a rare phenomenon for both Fe(II) and Fe(III) states with the same ligand.
• Complex 3 displayed three accessible electronic states (LS Fe(II)-LS Fe(III), HS Fe(II)-LS Fe(III), HS Fe(II)-HS Fe(III)).
• Complexes 1-3 demonstrated light-induced excited spin-state trapping at Fe(II) sites.

Conclusions:

• The study presents a rare example of spin crossover in both Fe(II) and Fe(III) complexes with a common tripodal ligand.
• The mixed-valence complex 3 exhibits rich electronic behavior and forms a homochiral 2D assembled sheet.
• The observed light-induced effects highlight the potential of these iron complexes in switchable materials applications.