Abrupt Spin Transition in a Heteroleptic Fe(II) Complex with Pendant Naphthalene Functionality

Area of Science:

• Coordination Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Spin-crossover (SCO) complexes are molecular materials that can switch between low-spin and high-spin states.
• Heteroleptic SCO complexes offer tunable properties through varied ligand combinations.
• Understanding ligand effects on SCO behavior is crucial for designing functional materials.

Purpose of the Study:

• To synthesize and characterize a new heteroleptic iron(II) SCO complex with tris(2-pyridylmethyl)amine (tpma) and 8,15-dihydrodiimidazo[1,2-a:2',1'-c]naphtho[2,3-f][1,4]diazocine (xnap-bim) ligands.
• To investigate the influence of crystallization conditions and solvent molecules on the SCO properties.
• To explore the spin transition behavior, including hysteresis and light-induced effects.

Main Methods:

• Synthesis of the heteroleptic iron(II) complex [Fe(tpma)(xnap-bim)](ClO4)2.
• Crystallization under various conditions to obtain different solvates (e.g., 1·2.25py·0.5H2O, 1·py).
• X-ray crystallography to determine crystal structures and packing.
• Variable-temperature magnetic susceptibility measurements to study spin transitions.

Main Results:

• Two distinct solvates and the solvent-free form of the complex were obtained.
• Crystal structures reveal double columns stabilized by π-π interactions.
• Solvent-free complex 1 exhibits an abrupt SCO transition at 127 K with a 2 K hysteresis.
• Light-induced excited spin state trapping (LIESST) effect observed at 5 K.

Conclusions:

• The synthesized heteroleptic complex displays tunable SCO behavior influenced by solvent molecules.
• The abrupt spin transition and narrow hysteresis in the solvent-free form are promising for bistable molecular devices.
• The observed LIESST effect highlights the potential for optical control of spin states.