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submitted on 07.08.2020 and posted on 10.08.2020by Airi Kawamura, Jiaze Xie, Jan-Niklas Boyn, Kate Jesse, Andrew McNeece, Ethan A. Hill, Kelsey Collins, Juan Valdez-Morreira, Alexander S. Filatov, Josh W. Kurutz, David A. Mazziotti, John Anderson
Organic diradicals are uncommon species that have been
intensely studied for their unique properties and potential applicability in a
diverse range of innovative fields. While there is a growing class of stable
and well characterized organic diradicals, there has been recent focus on how
diradical character can be controlled or modulated with external stimuli. Here
we demonstrate that a diiron complex bridged by the doubly oxidized ligand
tetrathiafulvalene-2,3,6,7-tetrathiolate (TTFtt2−) undergoes a
thermally induced Fe-centered spin-crossover which yields significant diradical
character on TTFtt2−. UV-vis-Near-IR, Mössbauer, NMR, and EPR
spectroscopies with magnetometry, crystallography, and advanced theoretical
treatments suggest that this diradical character arises from a shrinking TTFtt2−
π-manifold from the Fe(II)-centered spin-crossover. The TTFtt2− centered
diradical is predicted to have a singlet ground state by theory and variable
temperature EPR. This unusual phenomenon demonstrates that inorganic spin
transitions can be used to modulate organic diradical character.