Syntheses And Properties Of Coordination Polymers Or Metal-Organic Frameworks Based On The Pyridine Carboxylic Acid Ligand

The pyridine carboxylic acid ligand HL was synthesized using simple aldehydes and ketones,pyridine,imidazo[1,2-a]pyridine and other compounds.Different coordination polymers(CPs)or metal-organic frameworks(MOFs)are prepared by solvothermal reaction of the synthesized organic ligand and inorganic metal salts.The structure and properties of the coordination polymers can be adjusted by changing the reaction conditions such as the type of metal salts,the type and proportion of solvents,and temperature.The obtained coordination polymers are characterized by scientific testing methods,and the structures and properties of coordination polymers or metalorganic frameworks are explored by analyzing the spectra of nuclear magnetic resonance,infrared spectrum,fluorescence spectrum,single crystal diffraction spectrum,thermogravimetric analysis,etc.,and corresponding explorations are made in the properties and applications of luminescence,gas adsorption and desorption,and thermal stability.Under the same solvothermal conditions,nine novel coordination polymers(CPs),[Mn(L)(Cl)(H2O)](1a),[Mn(L)(H2O)2]·(NO3)(2a),[MnL]·(HSO4).MeCN·2H2O(3a),[Zn(L)2]·H2O(1b),[Zn(L)2](2b and 3b),[Cd(L)]·Cl(1c),[Cd(L)(NO3)](2c)and[CdL]-(HSO4)·2.5H2O(3c),were synthesized using a new ligand HL by changing metal cations or anions of inorganic metal salts.The Zn(Ⅱ)CPs lb-3b are similar 1D chains and their structures were mediated by the trigonal bipyramidal geometry of the Zn(Ⅱ)cation,not by the counter-anions.However,when using Mn(Ⅱ)and Cd(Ⅱ)salts bearing various counter-anions(Cl-,NO3-or SO42-)as reagents,the Mn(Ⅱ)(1a-3a)or Cd(Ⅱ)(1c-3c)CPs do reveal different structures,which were induced by different anions acting as either a coordinated anion or a counter-anion for balancing the charge of la3a or 1c-3c.When the larger NO3-anion replaced the Cl-anion,the 1D molecular box chain of 1a with a coordinated Cl-anion was changed to the 2D brickwall-type network of 2a with NO3-only as a counter-anion.However,the NO3-anion still could be coordinated to larger volume of the Cd(Ⅱ)cation,leading to a 3D framework for 2c.Moreover,CPs 3a and 3c are isostructural,which could be induced by the much larger tetrahedral HSO4-counter-anion.In addition,two new coordination polymers have been synthesized with new ligand HL,[Co(L)2]n(10)and {[Co3(L)4(NO3)2(H20)4]·2H2O}n(11),and two new novel isostructural metal-organic frameworks,{[Co(L)(NO3)(H2O)]·0.5H2O}n(12)and{[Ni(L)(NO3)(H2O)]·0.5H2O}n(13).The structure of 10-13 was tested and characterized.Their dimensionality ranges from two-dimensional networks(10 with a(4,4)network and 11 with a quasi-"long and short brick" network)to three-dimensional frameworks(isostructural 12 and 13).The dimensional/structural diversities are mediated by the solvation level of nitrate anions which was adjusted only via changing the solvent ratio(acetonitrile:water).Interestingly,compared to 10 and 11,12 and 13 display enhanced luminescence emission.The gas adsorption properties of 12 and 13 have also been investigated.