Structure And Properties Of Fe(Ⅲ) And Mn(Ⅲ) Spin Crossover Complexes Based On Hexdentate Schiff-base Ligands

Bistable molecular-based magnetic materials,such as Spin crossover（SCO）molecules,have attracted much attention due to their potential applications in molecular electronics and nanoscale devices.The transition between high-spin（HS）and low-spin（LS）states is driven by changes in external parameters（temperature,pressure,illumination,etc.）.Accompanied by changes in structure and properties,spin crossover materials have potential applications in data storage,display devices and other fields.Based on this,a series of Fe（Ⅲ）and Mn（Ⅲ）spin crossover complexes constructed by hexadentate Schiff-base ligands are designed and synthesized,and their structures,magnetic properties and electrochemical properties are characterized.The following research progress has been made:1.Anion-regulated Fe（Ⅲ）complex[Fe（5-F-sal-N-1,4,7,10）]X.To enrich the intermolecular interactions in the system,based on the hexadentate Schiff base（saltrien）^2–ligand,a fluorine substituent is introduced to obtain（5-F-sal-N-1,4,7,10）^2–ligands,and complexes 1-3 are synthesized with different anions.Structural and magnetic analyses are carried out with single crystal X-ray diffraction and magnetic measurements,supplemented by Heirsfield surface analysis.The results show that the magnetic behaviors of the three complexes are quite different,1 is an incomplete progressive spin crossover complex;the Fe1 center in the complex 2 undergoes complete spin transformation,and the Fe2 center has been kept in a high spin state;In complex 3,both Fe1 and Fe2centers are in high spin states between 2 and 400 K.The large difference in magnetic properties suggests that anions are valuable in regulating the spin-crossover properties of complexes.2.Study on halogen substituted Fe（Ⅲ）complex[Fe（5-X-sal-N-1,4,7,10）]Cl O₄.In order to study the effect of halogen substituents on spin crossover behavior,complex 4-7:[Fe（5-X-sal-N-1,4,7,10）]Cl O₄（X=F（4）,Cl（5）,Br（6）and I（7））were synthesized.Single-crystal X-ray analysis shows that there are two types of cations（Fe1 and Fe2）in the asymmetric unit of complex 4,while complexes5-7 contain only one type of cation.Magnetic analysis indicated that the two types of Fe（Ⅲ）centers in complex 4 experience different SCO behaviors,and complexes 5 and 6 remain in the LS state from2 to 300 K.Electrochemical analysis indicates that the ligand substitution affects the electron density at the metal center.In addition,IR spectra shows differences in the strength of hydrogen bonds between anions and cations in the complexes.Therefore,the spin-crossover behavior of the complex can be influenced by adjusting the ligand substituents.3.Anion-regulated Mn（Ⅲ）complex[Mn（5-Br-3-OMe-sal-N-1,5,8,12）]Y.Four hexadentate Schiff base complexes with different anions centered on Mn（Ⅲ）[Mn（5-Br-3-OMe-sal-N-1,5,8,12）]Y（Y=PF₆^–（8）,Br^–（9）,Cl^-（10）and Cl O₄^-（11））were synthesized.X-ray single crystal diffraction analysis shows that the packings of complexes 8–10 were similar,but the intermolecular interaction strengths and species are different.The volume of anions decreases from Br^–to Cl^–and the Mn···Mn distances become shorter,resulting in a tighter packing of complex 10.Magnetic analysis shows that complex 8 exhibits partial SCO behavior.It is proved that changing the anion is effective in regulating the magnetic properties of mononuclear Mn（Ⅲ）Schiff-base complexes.