Single-Chain Magnetic Property Tuning Via Photo-Induced Cyanide-Bridged Fe~??Co~? Charge Transfer

Single chain magnets(SCMs)exhibit bistable states and slow magnetic relaxation at a molecular scale,rendering them as the promising candidates for high-density information storage.It is a big challenge to control the generation and elimination of SCM behavior rapidly through light irradiation for the read-in and erasure of information.The thesis aimed to realize the light-switchable SCM properties.Based on the electron spin attribute and molecular engineering principles,the Fe-Co primitives were assembled in one dimensional chains,wherein the spin states and magnetic coupling actions could be controlled synergistically by the reversibly light-induced metal-to-metal charge transfer(MMCT).In addition,the effects of coordination configurations and intermolecular interactions were discussed.The main research results are as follows:(1)Electron-transfer complexes 1-3 were synthesized based on bidentate bridging ligands of bispyridine derivatives.1 and 2 underwent thermal-induced MMCT above room temperature,wherein the desolvated samples 1desolo showed ferromagnetism stable at high-spin state,and 2desolv exhibited an incomplete MMCT with a lower transition temperature associated with the variable temperature rate.3 showed a thermal-and light-induced Fe??Co? electron-transfer,synergistically generating light-actuated magnetic relaxation behavior under 808 nm laser.(2)Complexes 4-7a in neutral Fe2Co chains exhibited light-actuated SCM properties through light-induced MMCT under 808 nm laser,based on the monodentate pyridine derivatives controlling the N6 coordination configurations of Co2+centers and interchain stacking.The results show that increasing the deviation of the Co center from the octahedron is beneficial to the enhancement of magnetic anisotropy,and the conversion ratio of photo-responsive MMCT affects the magnetic coupling strength and the effective chain length after photo-excitation,which determine the magnetic relaxation process and energy barrier.The polymorphism 7b obtained by the crystal epitaxial growth of 7a showed ferrimagnetism,which provides a good molecular model for the structure-function study.It shows that the Fe—Co primitives tend to stabilize in {Fe?Ls(?-CN)Co?Hs}(LS=low spin;HS=high spin)state when the Co-N(?)C bond angle deviates from the linearity excessively.(3)Based on the results of the above studies,rigid auxiliary ligands 4-(4-R-phenyl)pyridine with different steric effects of the substituents(R=NO2,CF3)were selected for the synthesis of complexes 8-10,which effectively regulated the crystal packing.For the first time,8 exhibited on/off-switching SCM properties under alternating irradiation with 808 and 532 nm lasers through the reversibly light-switchable MMCT between diamagnetic{Fe?Ls(?-CN)Co?Ls} and paramagnetic {Fe?LS(?-CN)Co?Hs} pairs.Both 9 and 10 responsed to the light-induced Fe??Co? at 808 nm,leading to the photo-actuated SCM behavior.However,the photo-reverse Co??Fe? at 532 nm was observed partially in 9,but did not occurred in 10.The results demonstrated that the intermolecular interactions played a key role in the differences of the photo-switchable MMCT,which further affected the photo-switch of SCM properties.