Synthesis,Structure And Properties Of Spin Crossover Molecular Magnetic Materials

As well pential candidates in the application of molecular switch material,information storage and display material,spin crossover compounds with both important application prospect and theoretical significance have been paid more and more attention by the researchers in the material field all over the world.Therefore,the development of molecular switching devices and molecular mat erials related to real life become important goal in the field of spin crossover compounds.Based on this,we use[Hg(SCN)4]2-as the precursor,which has n ever been used in SCO field,combination with different bridging ligands,usin g different synthetic methods and crystallization methods,to design the optiona 1 crossover system.Furthermore,based-on the analysis of relationship between structure and properties,and for the aim of obtaining well behaved spin cross-molecular compound,we try to use different controling methods to tune the na ture of the spin state of the metal atom,and after that to discuss the factors t hat affect the spin state transition of the spin cross-compound,to further optim ize its magnetic properties.The main research contents are as follows:1.The reactions of transition metal Fe(?)compound,4,4 'bidentate pyridin e and its analogues acting as bridging ligands,including 4,4'bipy,bpe,tvp,4-a zpy,PQ,YXPJ,Pz,and[K2Hg(SCN)4]as precursor,have been carried out,an d seven novel Hg-Fe complexes have been synthesized by solvent diffusion me thod at room temperature,whose formulas are:{Fe?[(Hg?(SCN)3)2](4,4'bipy)2}(1);{Fe?[(Hg?(SCN)4)](bpe)2}n(2);{Fe?[(Hg?(SCN)3)2](azpy)2}n(3);{Fe?[(Hg?(S CN)4)](Pz)2}n(4);{Fe?[(Hg?(SCN)3)2](PQJ)2}n(5);{Fe?[(Hg?(SCN)3)2](YXPJ)2}n(6);{Fe?[(Hg?(SCN)3)2](tvp)2}n(7).The structures of the complexes were charac terized by IR and elemental analysis,and further confirmed by single crystal X-ray diffraction analysis.Single X-ray diffraction reveal that complexes 1,3-7 belong to the two-dimensional network structure,while the complexes 2 and 4 can be sturucturally characterized as three-dimensional network structures.The t emperature dependence of the magnetic susceptibility shows that complexes 1,5-7 are with spin crossover behaavior,in which complex 1 presents multiple st eps of spin crossover.As for the complexes 2 and 4,the spin state of Fe ato ms exhibits always high spin state within the temperature range from 300K-2K.The different structural type and spin crossover properties of these complexes f urther show that the length,rigidity and the coordination field of the organic b ridging ligand can put obvious effect on the dimensionality structure of the co mplexes formed.These examples provide new contribution to the study of the relationship between the structure and the nature of the spin crossover system,and also provide new idea for the designed synthesis of new spin crossover co mplexes.2.The reactions of transition metal Fe(?)compound,3,3'-bidentate pyridin e ligands including 3,3'-bipy and 3-azpy,and[K2Hg(SCN)4]as precursor,have been carried out,and two novel Hg-Fe complexes were assembled by solvent diffusion method at room temperature with the formula:{Fe?[(Hg?(SCN)4)](3,3'-bipy)2}n(1)and{Fe?[(Hg?(SCN)4)](3-azpy)2}n(2).The structures of the complexes were characterized by IR and elemental analysis,and further confirmed by sin gle crystal X-ray diffraction analysis.Single X-ray diffraction reveals that com plexes 1 and 2 are three-dimensional network structure.The temperature depen dence of the magnetic susceptibility shows that there is no spin crossover phen omenon in these two complexes.The structure and properties of these complex es further illustrate the structure and the steric effect of the organic bridging li gands have significant effect on the network dimension structure of the comple xes formed,and also on the spin state of the paramagnetic metal atoms.3.The reactions of transition metal Fe(II)compound,3-substituted pyridine ligands such as 3-Fpy,3-Brpy,3-Clpy,3-Ipy,and[K2Hg(SCN)4]as precursors,have been carried out,and four novel Hg-Fe complexes were synthesized by solvent diffusion method at the room temperature.Their formula are as follows:complex:{Fe?[(Hg?(SCN)4)](3-Fpy)2}n(1);{Fe?[(Hg?(SCN)4)](3-Clpy)2}n(2);{F e?[(Hg?(SCN)4)](3-Brpy)2}n(3);Fe?[(SCN)2)](3-Ipy)4(4).The structures of the co mplexes were characterized by IR and elemental analysis,and further confirme d by single crystal X-ray diffraction analysis.Single X-ray diffraction reveas th at complexes 1-3 belong to three-dimensional structure,while complex 4 is a mononuclear complex.The temperature dependence of the magnetic susceptibilit y shows that complex 1 is with spin crossover behavior with the spin state ch anged from HS to LS.For complex 2,because of the unconspicuous decline o f the magnetic susceptibility with the temperature lowering,it is difficult to ac curately confirm the spin crossover behavior.The complex 3 is with no SCO behavior with the high spin state of the Fe(II)within the temperature range fro m 300K-2K.4.The Schiff base ligand based-on dicyanylenetriamine and salicylaldehyde was combined with FeC13 and cyanide precursor K[Fe?(bpb)(CN)2],K[Co?(bp b)(CN)2],bipy and DMAP ligand,resulting in four complexes by solvent evapo ration.Their formulas are as follows:{[Fe?(bpb)(CN)2][Fe?(saldptn)]}CH3OH·H20(1);{[Co?(bpb)(CN)2][Fe?(saldptn)]}CH3OH(2);{[Fe?(saldptn)](DMAP)}B(C6H5)4(3);{[Fe?(saldptn)]2(bipy)}[B(C6H5)4]2(4).The structures of the complex es were characterized by IR and elemental analysis,and further confirmed by s ingle crystal X-ray diffraction analysis.Complexes 1,2,as well as complex 4,belong to binuclear structure,in which the metal centers are bridged by the c yanide bridge.For complex 4,the two metal centers are bridged by the N ato ms of the bidentate pyridine ligand.The iron atom in complex 3 is only conne cted to the N atom of the monodentate pyridine ligand,therefore forming mon onuclear structure.The temperature dependence magnetic susceptibility shows th at the complexes 1 and 2 are paramagnetic with no spin crossover phenomenon.Complexes 3 and 4 show obvious spin crossover phenomenon.The structure a nd properties of these complexes indicate that the difference of the field streng th between cyanide and pyridine ligand play an important role on the spin stat e of the metal atom and the magnetic behavior of the complexes formed.