Design,Syntheses And Properties Of Cyano-Bridged Mixed-valence Hexanuclear Iron (Ⅱ/Ⅲ) Clusters

In the 21st century,the reserch of new materials have been promoted by information technology which is developing rapidly.Due to the excellent properties of molecular based magnetic materials,these materials which are favored by researchers have a wide range of application prospects in high-density storage and other fields.In particularly,bistable magnetic molecules which can be switched by the stimulation of external conditions between two kinds of steady states,have the potential to be used in molecular switches,displays and memories.Among them,spin cross complexes,as an important research direction of bistable molecules,have been reported in a large number of literatures,most of which are Fe(Ⅱ)complexes,while Fe(Ⅲ)complexes are relatively few.In the construction of polynuclear complexes,the bridging ligand CN-shows its excellent properties.The cyano unit constructed by CN-can modularize the assembly of spin crossover molecules,which greatly facilitates the design and synthesis of such molecules.Inspired by the tetranuclear complex {[(Tp4-Me)FeⅢ(CN)3]2[FeⅡ(Tpa)]2}·2ClO4,we used[Ph3PMe][(Tp4-Me)FeⅢ(CN)3]as the cyano building unit,so four spin-crossover complexes were designed and synthesized.Through solvent diffusion,volatilization or exchange,{[Tp4-MeFeⅡ(CN)3]2[FeⅢ(Tpa)]2[FeⅢ(Tpa)(CH3O)]2}·(ClO4)6·8CH3OH(1),{[Tp4-MeFeⅡ(CN)3]2[FeⅢ(Tpa)]2[FeⅢ(Tpa)(CH3CH2O)]2}·(ClO4)6·6EtOH(2),{[Tp4-MeFeⅡ(CN)3]2[FeⅢ(Tpa)]2[FeⅡ(Tpa)(OH)]2}·(ClO4)6·7H2O(3),{[Tp4-MeFeⅢ(CN)3]2[FeⅡ(Tpa)]2[FeⅡ(Tpa)(CH3CN)]2}·(ClO4)6·6CH3CN(4)were synthesized and studied by X-ray single crystal diffraction,X-ray powder diffraction,infrared spectroscopy,electrochemical analysis and magnetic analysis.Although complexes 1-4 have similar structures,each of them has a distorted square lattice.Fe centers are connected by CN-,and the centers of Fe3 are outside of the lattice.Through the single crystal diffraction,variable temperature infrared spectroscopy and magnetic analysis,the valence state of Fel centers from complexes 1,2 and 3,in the N3C3 coordination environment of cyano building unit has been confirmed in positive bivalent,which is different from the common positive trivalent.These complexes exist in the form of FeⅢ-{FeⅡ2FeⅢ2}-FeⅢ.It can be inferred that valence transition occurred during selfassembly of[Ph3PMe][(TP4-Me)FeⅢ(CN)3]and Fe(ClO4)2.Three complexes show an unexpected spin-crossover phenomenon of FeⅢ and the spin transition is incomplete.The transition temperature T1/2 of complexes 1 and 2 is much higher than 300 K,while T1/2 for complexe 3 is about 150 K.Combine1d with the the variable temperature infrared spectrum of complex 1,there is no charge transfer occurred in the process of spin transition.However,complex 4 exists in the form of FeⅡ-{FeⅢ3FeⅡ2}-FeⅡ,which also exihibits spin-crossover phenomenon.