Synthesis And Catalytic Properties Of Coordination Polymers Based On Nitrogen/Carboxylate Ligands

Now,the design and synthesis of metal-organic coordination polymers based on the crystal engineering has become one of the most important ways to study in the fields of coordination chemistry and material chemistry.Due to their tunable structures and functionalities designed by the way of crystal engineering,Coordination polymers have potential applications in optics,electricity,catalysis,sensing,and gas storage and so on.However,in the field of catalyst,coordination polymers suffer from some problems.Such as low conversion and weak stability,etc.We have synthesized ten new coordination polymers based on nitrogen/carboxylate ligands by hydrothermal methods in this paper.Their structures have been characterized by X-ray single crystal diffractometer,X-ray power diffractometer,thermogravumetric analysis,IR spectra and element analysis.Moreover,the catalytic properties of 1,2,3 have also been studied through the selective oxidation experiments of hydrocarbons.1.By using mpca ligands(5-methyl-3-phenylisoxazole-4-carboxylic acid),bpp ligands(1,3-bis(4-pyridyl)propane)and Co/Zn/Cd metal center as additives,four coordination polymers had been obtained under hydrothermal conditions:Co(bpp)(mpca)2(1)Zn(bpp)(mpca)2(2)Cd(bpp)(mpca)2(3)Structural analysis revealed that compounds 1,2,3 had the similar 1D chains,and they also had the similar 2D supramolecular structure through hydrogen bonding.Catalytic experiments using 1,2,and 3 as catalysts indicated that all of the three compounds have predominant catalytic properties.Among 1,2,3,compound 1 exhibited the best catalytic activity.The conversion of cyclooctene was up to 45.77%with catalyst 1 after 48 h.And the selecyivity of epoxycyclooctane was up to 90.85%,while the selectivity of 2-cyclooctenone was up to 9.08%after 48 h.The reason of this phenomenon we guessed was that catalyst 1 exhibited different catalytic activities for epoxycyclooctane and 2-cyclooctenone.2,We chose ligands with many carboxyl groups as frist ligand,like 1,3,5-benzenetricarboxylic acid(BTC),1,2,4,5-benzenetetracarboxylic acid(BTEC)and 5-aminoisophthalic acid(AIPC).And the 1,3-bis(4-pyridyl)propane(bpp)was chosen as the second ligand as well as the Ni metal center as the additives,three coordination polymers had been obtained under hydrothermal conditions:Ni4(BTC)2(bpp)2·10H2O2(4)Ni(AIPC)(bpp)(5)Ni2(BTEC)(bpp)2-2H20(6)Structural analysis revealed that compound 4 exhibited three-dimensional frameworks through the parallel interpenetration of two adjacent layers connected by transition metal and two bridging ligands(BTC and bpp),while compounds 5 and 6 showed two-dimensional layered structures connected by transition metal and two bridging ligands.The selective oxidation experiments of cyclooctene with compounds 4,5,6 as catalysts indicated that all these three compounds exhibited unsatisfactory catalytic activities.Compound 4 exhibited the best catalytic activity.And the conversion of cyclooctene was just up to 13.17%.The reason of this phenomenon we guessed was that all three ligands BTC,BTEC,AIPC we chose showed low catalytic activities.3.The 1,2,4,5-benzenetetracarboxylic acid(BTEC)was chosen as the major ligand as well as the flexible 1,3-bis(4-pyridyl)propane(bpp)was chosen as the second ligand.And Co(Ac)2,NH4VO3 was chosen as metal center additives.Compounds 7,8,9 and 10 had been obtained under hydrothermal conditions:Co3(bpp)2(BTEC)2·10H20(7)Cos(bpp)(BTEC)2·2H20(8)Co3(V03)6(bpp)4·6H20(9)Co(VO3)2·2H20(10)Structural analysis revealed that compounds 7 showed the two-dimensional layered structures connected by transition metal and two bridging ligands(BTEC and bpp),while 8 exhibited three-dimensional frameworks connected by transition metal and two bridging ligands(BTEC and bpp).And 9 exhibited three-dimensional frameworks connected by transition metal,[VO3]-and bridging ligand bpp,while 10 exhibited three-dimensional frameworks connected by transition metal and[VO3]-.The selective oxidation experiments of cyclooctene with compounds 7,8,9,10 as catalysts indicated that the catalytic activities of compounds 9 and 10 with two metal centers were not better than 7 and 8 with only one metal center,but reduced a lot.Further,compound 10 even had no catalytic activity to the selective oxidation of hydrocarbon.The reason of this phenomenon was that metal center ions in coordination polymers were wrapped closely and couldn't contact with substrate,So that the catalytic activities of coordination polymers were reduced.