Guest Removal and External Pressure Variation Induce Spin Crossover in Halogen-Functionalized 2-D Hofmann Frameworks

Area of Science:

• Materials Science
• Coordination Chemistry
• Solid-State Chemistry

Background:

• Spin crossover (SCO) materials exhibit tunable magnetic properties based on temperature or pressure.
• Hofmann frameworks are a class of coordination polymers with potential applications in sensing and data storage.
• Halogen functionalization offers a route to modify the structural and electronic properties of SCO materials.

Purpose of the Study:

• To investigate the impact of halogen functionalization on the SCO behavior of 2-D Hofmann frameworks.
• To explore methods for inducing SCO transitions in these materials, such as guest removal and external pressure.
• To understand the interplay between structural factors (steric bulk, guest molecules) and SCO properties.

Main Methods:

• Synthesis of halogenated Hofmann frameworks ([FeII Pd(CN)4(thioX)2]·2H2O).
• Powder and single-crystal X-ray diffraction to analyze structural changes.
• Magnetic susceptibility measurements to determine SCO transitions.
• Application of external physical pressure to induce SCO.

Main Results:

• Halogenation and guest molecules induce chemical pressure, initially blocking SCO.
• Removal of solvent molecules or application of physical pressure (>0.62 GPa) restores cooperative one-step SCO transitions.
• Structural analysis reveals robust frameworks with minor variations between solvated and desolvated states.
• Transition temperature shifts observed between chloro- and bromo-analogues due to steric and electronic effects.

Conclusions:

• Halogenated Hofmann frameworks can be designed to exhibit controlled SCO behavior.
• Guest removal and external pressure are effective triggers for SCO transitions in these materials.
• The study highlights the importance of structural and electronic factors in tuning SCO properties for potential applications.