Construction And Magnetic Properties Of Tricyano-Bridged Molecule-based Magnets With Bistability

Molecule-based magnets with magnetic bistability have potential applications in the fields of high-density information storage and molecular switches,thus,the design and construction of molecule-based magnets with magnetic bistability is one of the hot topics in the fields of chemistry,physics and materials science.In this dissertation,the tricyanometalate building units are used to construct the molecule-based magnets with magnetic bistability.The main research strategies are as follows:(1)Introduction of building units and auxiliary ligands with different steric hindrances may realize the control of the chain-like topologies.Furthermore,the introduction of metal ions with anisotropy adjusts the intramolecular interactions to ferromagnetic interactions,realizing the construction of single-chain magnets.(2)Selecting the auxiliary ligands with similar structures is used to construct single-molecule magnets with tetranuclear structures,illuminate the assembly rules and reveal the magnetism-structure relationships.(3)Synthesis of charge transfer compounds,regulation of transition temperature and charge transfer behavior by external stimuli of light or heat are achieved by adjusting the coordination field and the redox potential of the metal centers through building blocks,auxiliary ligands and counterions.The main results are as follows:(1)Four cyanide-bridged 1D chain compounds were synthesized by the reaction of tricyanometalate[Bu4N][Fe(L)(CN)3](L = Tp,PzTp and Tp*)building units,bidentate ligands with different steric hindrances and transition metal Mn? and Co? ions.The magnetic interactions are adjusted by the structural distortions.The introduction of metal Co? ion with anisotropy results in the intramolecular ferromagnetic interaction,which realizes the construction of single-chain magnets.(2)Fifteen cyanide-bridged Fe?2Ni?2 tetranuclear compounds were synthesized by the reaction of bidentate ligands with similar structures and different steric hindrances and transition metal Ni? ion in the presence of the tricyanometalate building units.The magnetic data indicate that all compounds exhibit the ferromagnetic interactions.In the twelve compounds with single-molecule magnet behavior,compound 10a exhibits the highest energy barrier(?E/KB 83.9 K)for magnetization reversal seen for cyanide-bridged Fe?2Ni?2 tetranuclear compounds.Structure-magnetic property relationship indicates that the bistable relaxation energy barrier is closely related to the anisotropy of Fe? ion and the coordination environment of crystal field.(3)Three cyanide-bridged Fe2Co2 tetranuclear compounds were synthesized by the reaction of the same tricyanometalate building unit[Bu4N][Fe(Tp)(CN)3]and transition metal Co? ion and the impact of various 4,4'-disubstituted 2,2'-bipyridine ligands with the different electron-donating and electron-accepting groups(4,4'-dimethoxy-2,2'-bipyridine,4,4'-bis(N,N-dimethylamino)-2,2'-bipyridine and 4,4'-dichloro-2,2'-bipyridine)on the redox potential of Co? ions was researched.Structure-magnetic property relationship indicates that the HS Co? compound can be obtained when 2,2'-bipyridine ligand with the electron-accepting group is used.Seven cyanide-bridged Fe2Co2 tetranuclear compounds were synthesized by the reaction of the same bidentate ligand(5,5'-dimethy1-2,2'-bipyridine,pyrazino[2,3-f][1,10]phenanthroline and dipyrido[3,2-a:2',3'-c]-(6,7,8,9-tetrahydro)phenazine)and transition metal Co? ion and the impact of the tricyanometalate building units with the different structures on the redox potential of Fe?,ions was researched.The transition temperature for compound 15a is nearly at the room temperature(274 K).Structure-magnetic property relationship indicates that the trend of transition temperature is PzTp>Tp>Tp*when the same bidentate ligand is selected.Seven cyanide-bridged Fe2Co2 tetranuclear compounds were synthesized by the reaction of the same tricyanometalate building unit[Bu4N][Fe(PzTp)(CN)3]and bidentate ligand(pyrazino[2,3-f][1,10]phenanthroline)as well as transition metal Co? ion.The impact of counterions with different bulk(BF4-,PF6-and ClO4-)on the transition temperature of charge transfer compounds was researched.Structure-magnetic property relationship indicates that different counterions tune the intermolecular packing modes and interactions,which realize the control of transition temperature and thermal hysteresis.Compound 18·2CH3OH-4H2O including the solvent molecules is sensitive to external stimuli,which can transform into compound 18a by the two-step single-crystal to single-crystal transformations through desolvated and water vapor stimuli.Compound 18a exhibits a reversible electron-transfer behavior triggered by thermal treatment or alternative irradiation with different wavelength light.