Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover
Airi Kawamura, Jiaze Xie, Jan-Niklas Boyn, Kate A. Jesse, Andrew J. McNeece, Ethan A. Hill, Kelsey A. Collins, Juan A. Valdez-Moreira, Alexander S. Filatov, Josh W. Kurutz, David A. Mazziotti, John S. Anderson
Abstract
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.