| Coordination polymers（CPs）are an important class of materials,which are formed by the self-assembly of metal ions and ligands and have repetitive structures extending in one-,two-or three-dimensional directions.Coordination polymer has excellent structure and property adjustability,and are of great value in theoretical and applied research.This article utilizes formate and oxalate ligands to assemble with iron ions in the presence of organic amines with different structures and pyridines to obtain eleven new iron-based complexes.The crystal structure of eleven complexes was analyzed,and their structural phase transition,magnetic and electronic conduction properties were investigated.The specific content is as follows:1.Five metallic oxalic acid complexes were synthesized with oxalic acid and organic ammonium cation by solvothermal method:[（（C6H5）CH2N（CH3）3）Fe（C2O4）Cl2]n（1）,[（（C6H5）CH2NH（CH3）2）Fe（C2O4）Cl2]n（2）,[（（C6H5）CH2N（CH2CH3）3）Fe（C2O4）Cl2]n（3）,[（N-PYF）2Fe（C2O4）]n（4）（N-PYF=pyridin-4-ylmethyl formamide）,[（DPDP）2.5Fe2（C2O4）2·0.5H2O]n（5）（DPDP=2,5-di（pyridin-4-yl）-1,4-dihydropyrazine）.N-PYF is the reaction of 4-（aminomethyl）pyridine with formic acid to form N-（pyridin-4-ylmethyl）formamide,and DPDP is a 2,5-di（pyridin-4-yl）-1,4-dihydropyrazine generated by the in-situ cyclization reaction of two N-PYFs.Single crystal structure analysis shows that oxalic acid,chloride ions,and trivalent iron ions in 1,2,and 3 form one-dimensional zigzag anion chains,the cationic structure of organic ammonium regulates the stacking of anion chains in the compound and controls the final structure of the compound.Oxalic acid and divalent iron ions in 4 also form a zigzag one-dimensional chain,and N-PYF directly coordinates with Fe ions through pyridine groups.Increase the reaction time of 4 to obtain two-dimensional layered structure 5,which indicates that 5 is formed on the basis of further reaction of 4.In 5,DPDP connects the iron oxalate one-dimensional chain to form a Hoffman two-dimensional layer,and uncoordinated DPDP and water molecules are interspersed in a disordered form between the two-dimensional pores.Magnetic tests show that 1,4 and5 are antiferromagnet.Among them,5 has spin tilt behavior and the magnetic transformation temperature is 9 K.The field cool curves under different external fields show that 5 have variable magnetism.The results of PFM revealed the existence of ferroelectricity in the film of 1.2.Using oxalic acid and formic acid as co-ligands,six metal oxalic acid co-ligand complexes were synthesized by solvothermal method under different organic ammonium induction:[（（CH2CH3）2NHCH3）Fe（HCOO）（C2O4）]2n（6）,[（DPMPA）2Fe4（HCOO）4（C2O4）4·H2O]n（7）（DPMPA=2-（3-（dimethylammonio）propyl）-3,4,5,6-tetrahydropyrimidin-1-ium）,[（MTP）Fe（HCOO）（C2O4）]n（8）（MTP=3-methyl-3,4,5,6-tetrahydropyrimidin-1-ium）,[（ETP）Fe（HCOO）（C2O4）]n（9）(ETP=3,3’-（ethane-1,2-diyl）bis（3,4,5,6-tetrahydropyrimidin-1-ium）,[（（CH2CH3）2NHCH3）FeⅢFeⅡ（HCOO）4（C2O4）]n（10）,[（C5H5NH）2FeⅢFe2Ⅱ（HCOO）7（C2O4）]n（11）.Among them,DPMPA,MTP and ETP are formed by in-situ reaction of the corresponding organic amines and formates under acidic conditions.Structure analysis shows that 6-11 is a three-dimensional structure with oxalate and formic acid as co-ligand,and organic ammonium is located in the three-dimensional framework.The metal Fe ions in 6-9 are all coordinated with two oxalates and two formic acids.6 is the lon topology of{66}node,and 7-9 is the sqc6 topology of diamond type of{66}node.The metal Fe ions in10 coordinated with one oxalic acid and four formic acids to form a hexagonal boron nitride type sqc12 topological structure with{46;64}nodes.The Fe1 and Fe2 ions in 11coordinate with one oxalic acid and four formic acids,while the Fe3 ions coordinate with six formic acids,forming a cai topological structure of{46;53;6}2{48;54;63}nodes.It is worth noting that the reaction materials of 6 and 10 are the same,but due to different feed ratios,resulting in different structures.Among them,6 crystallizes in the orthogonal Pna21 space group in the ferroelectric phase（LTP）,and in the orthonormal Pnma space group of paraelectric phase（HTP）crystallization,it is shown that 6 is ferroelectric.DSC and dielectric tests show that 6 has obvious structural phase transition at T=68℃,and 8 has obvious phase transition at T=104℃.Magnetic testing shows that 6 and 8 are antiferromagnets with spin tilt behavior,and field cooling and zero field cooling reveal that the magnetic phase transition temperatures of 6 and 8 are19 K and 25 K,respectively.The variable temperature conductivity test of 6,7 and 10shows that the conductivity of the complex increases with the increase of temperature.The conductivity of 6 is about 1.02×10-6 S/m at 293 K,reaching 9.55×10-5 S/m at 353K.The conductivity of 7 is about 2.1×10-8 S/m at 293 K,reaching 2.04×10-6 S/m at 423K.The conductivity of 10 is about 1.41×10-7 S/m at 303 K,reaching 4.08×10-7 S/m at 423 K. |
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