Regulation of Multistep Spin Crossover Across Multiple Stimuli in a 2-D Framework Material

Area of Science:

• Materials Science
• Solid-State Chemistry
• Supramolecular Chemistry

Background:

• Two-dimensional Hofmann framework materials exhibit complex spin-crossover (SCO) properties.
• The elastic interactions within these frameworks are sensitive to guest molecules and external stimuli.
• Understanding the interplay between structural, spin, and elastic properties is crucial for materials design.

Purpose of the Study:

• To investigate the impact of external stimuli on the structural, SCO properties, and elastic interactions of [Fe(cintrz)₂Pd(CN)₄]·guest.
• To explore how guest molecule manipulation regulates the ferro- and antiferro-elastic balance.
• To identify mechanisms for overcoming elastic stabilization of mixed spin-state species.

Main Methods:

• Synthesis and characterization of the Hofmann framework material [Fe(cintrz)₂Pd(CN)₄] with varying guest content (3H₂O, 2H₂O, Ø).
• Investigation of spin-crossover properties under external stimuli: guest removal, light irradiation (reverse LIESST), and hydrostatic pressure.
• Analysis of elastic interactions using experimental data combined with elastic models.

Main Results:

• Guest molecule content (3H₂O, 2H₂O, Ø) significantly influences the ferro- and antiferro-elastic interaction balance.
• The mixed spin-state {HS-LS} is stabilized by antiferroelastic interactions in the presence of 3H₂O guest molecules.
• Guest removal, reverse LIESST (830 nm), and hydrostatic pressure can overcome elastic strain, altering the spin-state stabilization.

Conclusions:

• Guest molecules in Hofmann frameworks exert a negative chemical pressure and influence elastic interactions beyond simple pressure effects.
• The elastic interaction strain plays a critical role in stabilizing specific spin states.
• External stimuli offer effective routes to tune SCO behavior and elastic properties in these materials.