| With the development of science and technology,the research on the molecule-based magnets has attracted more and more attention.The magnetic materials with bistability have been a hot topic due to their fundamental importance and unique potential applications in the light/heat switching and information storage devices.According to the difference of electronic state response to external conditions,the bistable molecular-based magnetic materials can be divided into spin-crossover materials and molecular nanomagnets.We will mainly study the spin-crossover complexes and the single ion magnet,especially the Co ?single ion magnet.We have introduced some multi-functional units,such as tetrathiafulvalene unit,naphthalene diimide unit and trisphenylamine unit.We have synthesized a series of Schiff-base ligand and bidentate or multidentate bridging ligand,and sixteen novel coordination polymers were obtained by self-assembling.The syntheses,structural characterization,redox activity,magnetic properties and electrical of these coordination polymers were studied.The main achievements of this work are listed as below:1.Studying on the properties of Fe ?coordination polymers supported by Schiff-base ligand modualtionsA series of iron(?)coordination polymers,named[Fe ?(L1)(4-abpt)](1),[Fe ?(L2)(4-abpt)](2),[Fe 2?(L3)2(4-abpt)·Me OH]·[Fe ?(L3)(4-abpt)](3),[Fe 3?(L4)3(4-abp t)2·H2O](4)),with tetradentate Schiff-base like equatorial ligands(H2L1=3,3'-((1,2-phenylenebis(azanediyl))bis(methanylylidene))bis(pentane-2,4-dione),H2L2=diethyl2,2'-((naphthalene-2,3-diylbis(azanediyl))bis(methanylylidene))(2E,2'E)-bis(3-oxobut anoate),H2L3=diethyl 2,2'-((1,2-phenylenebis(azanediyl))bis(methanylylidene))(2E,2'E)-bis(3-oxobutanoate),H2L4=diethyl-2,2'-(((4,5-difluoro-1,2-phenylene)bis(azanediyl))bis(methanylylidene))(2E,2'E)-bis(3-oxobutanoate))and 4-abpt(3,5-di(pyridin-4-yl)-4H-1,2,4-triazol-4-amine)as a bidentate bridging axial ligand were obtained.In these complexes,the methanol molecules in the precursor[Fe ?(L)(Me OH)2]were replaced by bridging ligand(4-abpt)successfully,and all of which were one-dimensional(1D)chain structures.The central atom Fe ?adopts a distorted octahedron where two nitrogen atoms and two oxygen atoms from the Schiff-base form the basal plane,and two nitrogen atoms from the bridging 4-abpt occupy the axial positions.Each nitrogen atom from py bridges two Fe ?to construct linear 1D···Fe-py-Fe-py···chains.Magnetic measurements reveal that 1 is a typical low-spin compound.2 is a paramagnetic material,and 3 posseses a one-step spin transition(T1/2=115 K).While 4 features two-step spin transitions(T1/2=188 K and95 K)at higher temperatures.The conductivity results show that all of these compounds exhibit conducting-like behaviors.The results of the variable temperature susceptibility and the variable temperature conductivity of compounds 1-4 indicate that there may be some interaction between spin crossing and conductivity.In a Fe ?system,the co-existence of spin crossing and conductivity provides the possibility for the study of multifunctional materials.2.Studying on the properties of Fe ?coordination polymers based on tetrathiafuvalene unitIn this chapter,we have introduced the tetrathiafulvalene(TTF)unit with redox activity.Six iron(?)coordination polymers,named[Fe ?(LSchiff-base)(TTF-(i-ql)4)0.5]n(5-9)and[Fe ?(L7)(bpy)]n(10),with tetradentate Schiff-base like equatorial ligands((H2L1,H2L3,H2L4,H2L5=diethyl 2,2'-(((4-fluoro-1,2-phenylene)bis(azanediyl))bis(methanylylidene))(2E,2'E)-bis(3-oxobutanoate),H2L6=diethyl-2,2'-(((4,5-dibromo-1,2-phenylene)bis-(azanediyl))bis-(methanylylidene))-(2E,2'E)-bis-(3-oxobutanoate),H2L7=diethyl 2,2'-(((2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)benzo[d][1,3]dithi ole-5,6-diyl)bis(azanediyl))bis(methanyclylidene))(2E,2'E)-bis(3-oxobutanoate)),and redox-active TTF building block,TTF-(i-ql)4,(4,4',5,5'-tetra(isoquinolin-6-yl)-2,2'-bi(1,3-dithiolylidene))and bpy(4,4'-bipyridine)as a flexible bridging axial ligand were obtained and characterized by fundamental chemical methods.The thermal stabilities up to 200°C.In compounds 5-9,the methanol molecules in the precursor[Fe ?(L)(Me OH)2]were replaced by bridging ligand(TTF-(i-ql)4)successfully,and all of which were two-dimensional(2D)network structures.And these structures are stabilized in the crystal lattice through several hydrogen bonds and non-classical hydrogen bonds.The central atom Fe ?adopts a distorted octahedron where two nitrogen atoms and two oxygen atoms from the Schiff-base form the basal plane,and two nitrogen atoms from the bridging TTF-(i-ql)4occupy the apical positions.Compounds 5-9 display the incomplete spin transition behaviors and T1/2=350 K.And the solid state cyclic voltammetry(CV)results of compounds 5 and 6 suggested that the redox activity of ligand was well maintained in these complexes.While compound 10 is a typical one-dimensional(1D)chain structure,the central atom Fe ?also adopts a distorted octahedron.Each nitrogen atom from py bridges two Fe ?to construct linear 1D···Fe-bpy-Fe-bpy···chains,and short S···S contacts between the TTF moieties of adjacent parallel chains,leading to ladders.Intermolecular interactions(C2···O1)result in a 2D network.The magnetic susceptibility data of 10suggest that it shows a thermal hysteresis loop(8.1 K),and T1/2?=326.6 K,T1/2?=334.7 K.The most important is that unexpected coupling between spin-crossover and dielectricity enhancement.And this phenomenon is attributed to the bending of TTF elements at high temperatures.Moreover,the solid state cyclic voltammetry(CV)results of 10 suggest that the redox activity of ligand was well maintained in this compound.3.Studying on the properties of Fe ?coordination polymers based on naphthalene diimide unitIn this chapter,we have introduced another redox-active unit,naphthalene diimide(NDI)unit.Two iron(?)coordination polymers,named[Fe ?(L1)(NDI-py)]n(11)and[Fe ?(L3)(NDI-py)]n(12),with tetradentate Schiff-base like equatorial ligands(H2L1,H2L3)and redox-active NDI building block,NDI-py,(di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide)as a flexible bridging axial ligand were obtained and also characterized by fundamental chemical methods.In compounds 11-12,the methanol molecules in the precursor[Fe ?(L)(Me OH)2]were replaced by bridging ligand(NDI-py)successfully,and all of which were one-dimensional(1D)chain structures.And the central atom Fe ?adopts a distorted octahedron where two nitrogen atoms and two oxygen atoms from the Schiff-base form the basal plane,and two nitrogen atoms from the bridging NDI-py occupy the axial positions.Each nitrogen atom from py bridges two Fe ?to construct linear 1D···Fe-py-Fe-py···chains.Magnetic measurements reveal that 11 is a paramagnetic material,and 12 displays the complete spin transition behaviors and T1/2=300 K.At the same time,we study the thermal stability,conductivity,magnetic properties and potential application of these materials.The modulation of Schiff-base ligands will lead to the difference of coordination environment of metal center.And this would change the magnetic properties of coordination compounds.4.Studying on the properties of trisphenylamine-based coordination polymersIn this chapter,we have introduced a new functional unit,trisphenylamine unit.It is an efficient approach to exploit the pillaring and templating strategy for creating varieties of functionalized coordination polymers.Four novel coordination polymers incorporating single metal nodes and redox-active tris(4-(pyridine-3-yl)phenyl)amine ligand,m-NPy3,have been prepared by a hydrothermal method.Compounds 13-15,[M(m-NPy3)(NO3)2·CH3OH]n(M=Co for 13,Ni for 14,Zn for 15),are isomorphous two-dimensional(2D)layered coordination polymers.And the central Co ?ion is seven-coordinated by four oxygen atoms from two independent NO3?ions and three nitrogen atoms from three separate m-NPy3ligands.Horizontally,the ordered linking of these two dinuclear complexes formed the one-dimensional(1D)chain-like structure.And this 1D chain consists of a series of pores,where the shortest distance of each pore is 10.60?.Vertically,each 1D chain is linked by the m-NPy3ligand constructing 2D network,in which the shortest distance of the pore is 15.04?.These individual networks were interpenetrated with each other to form a 3D structure where channels can be observed.Compounds 14 and 15 show similar structures but different aperture size in the 2D plane.These sizes are 13.93?and 14.13?in 14 and15,respectively.Compound 16,[Co(m-NPy3)(TPA)0.5Cl·CH3OH]n(TPA=bidentate terephthalic acid),is a three-dimensional(3D)coordination polymer,which is pillared by linear bidentate terephthalic acid(TPA)linkers.Compound 16 can be obtained either by the“one-pot method”or by the solid-state single-crystal-to-single-crystal(SC-SC)transformation from compound 13 pillaring and templating strategy.The Co ?center in 16 is situated in a twisty octahedral coordination sphere consisting of two oxygen atoms from half TPA ligand bound in a bidentate fashion,three nitrogen atoms from three separate m-NPy3ligands and one chloride ion from Co Cl2·6H2O molecule.Compound 16 is different from the compound 13,in which the two aperture sizes of the single 2D network is 14.29?and 9.89?.These sizes are much smaller than that of 13,which may account for the coordination of TPA“pillars”.All of compounds were characterized by fundamental chemical methods.The results of solid-state cyclic voltammetry show that the redox activity of trisphenylamine is remained in these four coordination polymers.Compared with 13,the location of the first oxide peak in 16 shows a reduction of nearly 0.14 V vs Fc/Fc+.The magnetic studies shows that both compounds 13 and 16 exhibits the typical field-induced single-ion magnet behavior.In addition,compound 16 shows better magnetic performance compared with 13.Although both of them have the same magnetic centers,Co ?ion,13 has a distorted seven-coordinated Co ?ion,while 16adopts a twisted octahedral coordination sphere.The different coordination environments of central Co ?ion may be a crucial reason for their different magnetic properties. |
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