Reversible on–off switching of a single-chain magnet via single-crystal-to-single-crystal transition and light-induced metal-to-metal electron transfer†

The development of single-chain magnets with reversible and adjustable properties is of great significance for achieving high-density information storage and switching devices with multi-stimuli responsiveness, but it remains a challenging task. In this work, we synthesized a new cyano-bridged {Fe₂Co}-based coordination polymer, {[(^PzTp)Fe(CN)₃]₂Co(Ipi)₂}·2MeOH·0.5H₂O (1·solv; ^pzTp, tetra-kis(1-pyrazolyl)borate; Ipi, 1-(4-iodophenyl)-1H-imidazole). 1·solv displayed 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 irradiations with 808 and 532 nm lasers, respectively, as verified by photomagnetic and in situ photo-monitored X-ray diffraction studies. The bidirectional light irradiations induced significant changes in magnetic anisotropy and intrachain exchange interactions, demonstrating the on/off switching of single-chain magnet (SCM) behavior by 808 and 532 nm light irradiations. 1·solv underwent a thermally induced single-crystal-to-single-crystal (SCSC) phase transition into a desolvated {[(^PzTp)Fe(CN)₃]₂Co(Ipi)₂} (1·desolv) phase, accompanying MMET. Magnetic susceptibility measurements indicated that 1·desolv exhibited thermally induced incomplete MMET behavior and field-induced nanomagnet behavior. 1·desolv also displayed a substantial dielectric anomaly during the electron transfer process, presenting a new case showing the synergetic switching of the dielectric and magnetic properties. Interestingly, 1·desolv can revert to the solvated phase 1·resolv after being soaked in mother liquor, whose SCM behavior was erased by the reversible SCSC transition. This study provides a new approach for the swift and reversible control of SCM behavior via both SCSC transition and light-induced MMET.