Guest Programmable Multistep Spin Crossover in a Porous 2-D Hofmann-Type Material

Area of Science:

• Materials Science
• Solid-State Chemistry
• Coordination Chemistry

Background:

• Spin crossover (SCO) materials exhibit switchable properties driven by cooperative transitions.
• Multistep SCO transitions are desirable for data storage but require controlled elastic interactions.
• Antagonistic interactions, such as competing ferro- and antiferro-elastic forces, can drive complex lattice distortions.

Purpose of the Study:

• To synthesize and characterize a new SCO framework, [FeII(bztrz)2(PdII(CN)4)]·n(guest), capable of supporting antagonistic interactions.
• To investigate the influence of guest exchange on the SCO behavior within this framework.
• To explore the relationship between elastic frustration and the nature of spin transitions.

Main Methods:

• Synthesis of the 2-D Hofmann-type SCO framework [FeII(bztrz)2(PdII(CN)4)]·n(guest).
• Characterization of the material's structure and its dual guest pore system.
• Investigating SCO behavior through guest exchange experiments and analysis of spin transition characteristics.

Main Results:

• The synthesized material exhibits intrinsically frustrated SCO behavior due to competing ferro- and antiferro-elastic interactions.
• Guest exchange successfully modulated the SCO behavior, yielding one-, two-, and three-stepped transitions, as well as SCO-deactivation.
• The degree of elastic frustration and resulting spin transition complexity are tunable via molecular guest manipulation.

Conclusions:

• The new SCO framework demonstrates a versatile platform for achieving diverse spin transition behaviors.
• Elastic frustration, manipulated by guest molecules, is a key factor in controlling multistep SCO switching.
• This work suggests that subtle structural features contribute to multistep switching in SCO materials, opening new avenues for materials design.