Pressure-Induced Spin Crossover at Room Temperature in a Nanoporous Host-Guest Framework Structure

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Two-dimensional (2D) metal-organic frameworks (MOFs) exhibit unique properties.
• Spin crossover (SCO) in metal-ion sites is a key phenomenon in MOFs.
• Guest molecule inclusion can modulate MOF properties.

Purpose of the Study:

• Investigate pressure-induced spin crossover in a 2D MOF.
• Determine the effect of different guest molecules (isopropanol, ethanol) on SCO.
• Explore guest-specific triggering of spin crossover at room temperature.

Main Methods:

• High-pressure experiments using isopropanol and ethanol as pressure-transmitting media.
• Synthesis and characterization of the 2D MOF compound Fe₂(azpy)₄(NCS)₄.
• Analysis of spin state conversion (high-spin to low-spin) under pressure.

Main Results:

• Isopropanol inclusion induced ~66% low-spin abundance at ~3 GPa.
• Ethanol inclusion resulted in ~56% low-spin abundance at ~5.5 GPa.
• Achieved significant low-spin states at room temperature, comparable to low-temperature results at ambient pressure.

Conclusions:

• Pressure-driven guest molecule uptake triggers spin crossover in a guest-specific manner.
• Guest-molecule interactions with the Fe(II) coordination network enhance the ligand field.
• This study demonstrates a novel method for achieving spin crossover at room temperature using pressure and guest molecules.