A Ferric Semiquinoid Single-Chain Magnet via Thermally-Switchable Metal-Ligand Electron Transfer

We report the synthesis of a semiquinoid-bridged single-chain magnet, as generated through a thermally induced metal ligand electron transfer. Reaction of FeCl3 with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (LH2) in the presence of (NMe4)Cl gave the compound (NMe4)(2)[LFeCl2]. Together, variable-temperature X-ray diffraction, Mossbauer spectra, Raman spectra, and dc magnetic susceptibility reveal a transition from a chain containing (L2-)Fe-II units to one with (L3-center dot)Fein upon decreasing temperature, with a transition temperature of T-1/2 = 213 K. The dc magnetic susceptibility measurements show strong metal radical coupling within the chain, with a coupling constant of J = -81 cm(-1), and ac susceptibility data reveal slow magnetic relaxation, with a relaxation barrier of Delta(tau) = 55(1) cm(-1). To our knowledge, this compound provides the first example of a semiquinoid-bridged single-chain magnet.