Unravelling the spin-state of solvated [Fe(bpp)₂]²⁺ spin-crossover complexes: structure-function relationship

Area of Science:

• Coordination Chemistry
• Materials Science
• Magnetochemistry

Background:

• Spin crossover (SCO) complexes exhibit distinct low-spin (LS) and high-spin (HS) states.
• Lattice solvent molecules can significantly impact the SCO properties of metal complexes.
• Understanding solvent effects is crucial for designing SCO materials with tunable properties.

Purpose of the Study:

• To synthesize and characterize novel spin crossover salts: [Fe(bpp)2]3[Cr(CN)6]2·13H2O (1) and [Fe(bpp)2][N(CN)2]2·H2O (2).
• To investigate the influence of lattice water on the thermal and magnetic properties of these SCO salts.
• To elucidate the magneto-structural correlations governing the stabilization of LS or HS states by lattice solvents.

Main Methods:

• Single-crystal X-ray diffraction for structural analysis.
• Thermogravimetric analysis (TGA) to study desolvation and thermal transitions.
• Variable-temperature magnetic susceptibility measurements to probe spin crossover behavior.

Main Results:

• Compounds 1 and 2 feature hydrogen-bonded networks with [Fe(bpp)2]2+ complexes and various anions.
• Desolvation of compound 1 induces a reversible LS to HS spin transition upon rehydration.
• Magneto-structural correlations reveal that lattice solvent interactions (hydrogen bonding, π-π stacking) dictate LS/HS state stabilization.

Conclusions:

• Lattice water plays a critical role in modulating spin crossover behavior in [Fe(bpp)2]X2 salts.
• The nature of the anion and its interactions within the crystal lattice determine the SCO response.
• This work provides insights into the rational design of SCO materials by controlling intermolecular interactions.