Electron-Transfer-Induced Structural Modification in a Thermochromic Hofmann Clathrate Derivative

This study explores a Hofmann-type clathrate, {Fe₂(2,4-(OCH₃)₂-pbpy)₂(H₂O)₂[μ₂-Pt(CN)₄][μ₃-Pt(CN)₄]₂·4H₂O}, which exhibits a thermally activated electron transfer (ET) without spin crossover. Synthesized as microcrystalline powders and single crystals, this compound reveals significant structural changes upon variation of the temperature, including alterations in the iron coordination sphere due to the large movement of the bipyridinium ligand. These changes correlate with a thermochromic hysteretic transition from yellow to orange. Detailed characterizations using X-ray diffraction and IR spectroscopy indicate the involvement of nonbridging CN^- moieties as electron donors and bipyridinium units as acceptors. This result deepens our understanding of ET in Hofmann-type clathrates.