Discrimination between two memory channels by molecular alloying in a doubly bistable spin crossover material

Area of Science:

• Materials Science
• Solid-State Chemistry
• Supramolecular Chemistry

Background:

• Spin crossover (SCO) materials exhibit bistability, transitioning between low-spin and high-spin states.
• Controlling SCO events and associated phase transitions (PTs) is crucial for developing molecular switches and memory devices.
• Molecular alloys offer a platform to fine-tune SCO properties through compositional variations.

Purpose of the Study:

• To synthesize and characterize a novel multistable spin crossover (SCO) molecular alloy system: [Fe_1-xM_x((nBu-im)₃(tren))](P_1-yAs_yF₆)₂.
• To investigate the influence of isomorphous substitution (M = Zn^II, Ni^II; P/As anions) on SCO behavior and structural phase transitions.
• To demonstrate the ability to select and control distinct SCO events and hysteresis widths by tuning alloy composition.

Main Methods:

• Synthesis and characterization of the isomorphous SCO molecular alloy series.
• Magnetic and calorimetric measurements to probe SCO events and phase transitions.
• Single crystal and powder X-ray diffractometry to analyze structural changes.

Main Results:

• The 100As derivative exhibits a two-step SCO with two reversible structural phase transitions (PTs), including a low-temperature PT (PT^LT) coupled with SCO.
• The 100P derivative shows two distinct one-step SCO events controlled by temperature scan rates, linked to the kinetics of PT^LT.
• Hydrostatic pressure (0.1 GPa) interconverts the SCO behaviors of 100P and 100As, highlighting the role of chemical pressure.
• Controlled P/As substitution selects specific SCO memory channels, while Zn^II/Ni^II substitution favors a low-temperature memory channel.

Conclusions:

• The synthesized SCO molecular alloy system allows for precise control over cooperative SCO events and hysteresis via compositional tuning.
• The interplay between structural phase transitions, SCO, and isomorphous substitution dictates the material's multistable behavior.
• This work provides a pathway for designing advanced molecular materials with tailored thermal switching and memory functionalities.