Congratulations to Mengjia Shang for having her research accepted by INORGANIC CHEMISTRY.——Reversible on–off switching of a single-chain magnet via single-crystal-to-single-crystal transition and light-induced metal-to-metal electron transfer

Photo-responsive single-chain magnets (SCMs) featuring multi-switchable properties have long been a hot research topic owing to their promising application in high-density information storage and spintronic devices. In particular, the combination of this switchable magnetic property with dielectric property in SCMs is very important for intriguing device applications. However, it is still a formidable challenge to design bidirectionally light-driven SCMs with multi-stimuli responsiveness. Metal-to-metal electron transfer (MMET) can be switched by various external stimuli and is believed to be a good candidate to achieve this goal. In this work, we desgined a new cyano-bridged {Fe₂Co}-based coordination polymer, {[(^PzTp)Fe(CN)₃]₂Co(Ipi)₂}·2MeOH·H₂O (1·solv; ^pzTp, tetra-kis(1-pyrazolyl)borate; Ipi (1-(4-iodophenyl)-1H-imidazole). 1·solv displays reversible metal-to-metal electron transfer (MMET) between Fe^III_LS(μ-CN)Co^II_HS(μ-NC)Fe^III_LS (LS, low spin; HS, high spin) and Fe^III_LS(μ-CN)Co^III_LS(μ-NC)Fe^II_LS states under alternating irradiation with 808 and 532 nm lasers. The bidirectional light irradiations induce significant changes in anisotropy and intrachain magnetic interactions, thus realizing the on/off switching of SCM behavior by 808 and 532 nm light irradiations. In addition, 1·solv undergoes a solvent-induced single-crystal to single-crystal (SCSC) phase transition to a desolvated {[(^PzTp)Fe(CN)₃]₂Co(Ipi)₂} (1·desolv) accompanied by MMET, which can be attributed to changes in the Fe redox potential caused by the disruption of hydrogen bonds. Magnetic susceptibilities measurements indicate that 1·desolv exhibits thermally induced incomplete MMET behavior and field-induced nanomagnet behavior. 1·desolv displays a substantial dielectric anomaly during the electron transfer process, presenting a new example showing the synergetic switching of dielectric and magnetic properties. Interestingly, 1·desolv can revert to 1·resolv after soaking in the mother liquor, exhibiting a reversible SCSC transition-switched SCM properties.