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Evidence for surface effects on the intermolecular interactions in Fe(II) spin crossover coordination polymers
Thilini K Ekanayaka1, Hannah Kurz2, Kayleigh A McElveen3
1Department of Physics and Astronomy, University of Nebraska, Jorgensen Hall, Lincoln, NE 68588-0299, USA. thiliniek@huskers.unl.edu.
Physical Chemistry Chemical Physics : PCCP
|December 15, 2021
Summary
Surface spin crossover behavior in iron(II) coordination polymers differs from the bulk. Surface properties vary due to oxidation, packing, or coordination changes, impacting spin state transitions.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Surface Science
Background:
- Spin crossover (SCO) materials exhibit a change in spin state, typically from high-spin to low-spin, in response to external stimuli like temperature or pressure.
- The behavior of SCO materials at the nanoscale, particularly at the surface, can deviate significantly from their bulk properties.
- Understanding these surface effects is crucial for designing and applying SCO materials in devices.
Purpose of the Study:
- To investigate the spin state transition behavior of Fe(II) spin crossover (SCO) coordination polymer crystallites at the surface.
- To compare the surface spin state transition with the bulk behavior across different SCO materials.
- To identify factors contributing to the observed differences between surface and bulk properties.
Main Methods:
- Utilizing X-ray absorption spectroscopy (XAS) to probe the electronic structure and oxidation states.
- Employing X-ray photoemission spectroscopy (XPS) for surface-sensitive elemental and chemical state analysis.
- Synthesizing and characterizing four distinct Fe(II) SCO coordination polymers.
Main Results:
- XAS and XPS data reveal that the spin state transition of Fe(II) SCO crystallites at the surface is distinct from the bulk.
- A range of surface behaviors were observed, including complete spin switching, no switching, or intermediate states.
- Factors such as surface oxidation, altered molecular packing, and changes in coordination environment were identified as potential causes for surface-bulk discrepancies.
- Photoactivity of some SCO materials under X-ray irradiation complicated the discernment of intrinsic spin state transitions.
Conclusions:
- The surface spin state transition of Fe(II) SCO coordination polymers can differ substantially from their bulk counterparts.
- Surface properties are influenced by a combination of intrinsic material characteristics and extrinsic factors like sample preparation and measurement conditions.
- Further research is needed to fully elucidate the interplay between surface phenomena and spin crossover behavior for targeted applications.
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