Synthesis,Structure And Properties Of Bipyridinium Derivatives Based Porous Coordination Polymers

As a new class of organic-inorganic hybrid materials with unparalleled diversified,designable and tailorable structures as well as unique chemical and physical properties,the metal-organic frameworks(MOFs)have become one of the most important research topics in the field of chemistry and materials science.In this paper,we have employed photo/electrochemical activated flexible bipyridinium derivatives as functional ligands,together with transition-metal ions,through volatilization and solvothermal methods,to obtain five novel porous coordination polymers.We also used a cobalt-based porous coordination polymer as precursor to afford a series of porous carbon materials for for application in oxygen reduction reaction.The research contents are as follows:(1)The flexible bipyridinium ligands pbpy-2Cl-and pbpy·2ClO4-with Lewis acidic sites has been introduced to coordinate with terephthalic acid,Cd2+and halogen anions(Cl-/Br/I-)to yield four isomorphous porous coordination polymers(1,2,3 and 4)with 3-connected(103)ths(ThSi2-type)topology through solvothermal methods.Compounds 1 and 2 exhibit sensitive luminescent changes to achieve the selective sensing of ammonia molecules with Lewis base character,and can be designed as colorimetric change or on-off switching chemosensors.Compounds 3 has been constructed through precise coordination environmental control by using a flexible bipyridinium derivative and the iodine anion,which exhibits fast response(five seconds)to ammonia vapor accompanied by a triggered high-contrast color change from white to yellow that can be easily detected by naked eyes.This process is attributed to competitive complexation of ammonia as well as the combination of dissociated iodine ionic with bipyridinium radicals,which can form a novel intracomplex to strengthen the intramolecular charge transfer effect.Compound 4 contains both Cl-and Br-as coordination ions.These four isomorphous porous coordination polymers possess 1D channel with positively charged surface,which shows high affinities to polar molecules such as methanol,ethanol,and water vapor.Additionally,the cagelike pore space formed by these flexible bipyridinium molecules contains arene-arene stacked pyridyl rings and thus renders abundant π-πinteraction sites for efficient adsorption of benzene and toluene molecules,and is also large enough to accommodate cyclohexane molecules,displaying rarely broad-spectrum adsorptivity to various organic pollutants.Furthermore,the introduction of different coordinated halogen ions can not only achieve the purpose of structural controling,but also can affect the adsorption of guest molecules through the "anion-π" host-guest interaction.(2)A bipyridinium-based Borromean entangled porous framework(5)was found to be sensitive to both Cu Ka and Mo Ka Xray sources,showing rapid photochromic response and recovery within one minute.The X-ray-induced photochromic process is accompanied by a reversible single-crystal-to-singlecrystal(SC-SC)structural transformation,an unprecedented phenomenon for X-ray sensitive materials.The complex can be further processed into portable thin films for detecting the dose of the X-ray exposure as low as 7.72 Gy.Moreover,the photochromism can occur over a broad temperature range of 100-333 K,both in the form of single crystals and thin films,making it a potential candidate for practical indoor and outdoor applications.(3)A cobalt-based porous coordination polymer was used as precursor to afford a series of Co,N,O-doped porous carbon materials CoNOC-Tc-t(where Tc represents the carbonization temperature and t represents the carbonization time),which possess high surface area,hierarchically micro-,meso-and macropores,and high graphitization as well as the uniformly enchased N-Co-O catalytic active sites derived from pyridine nitrogen atom and chelating carboxylate coordinated octahedral cobalt(Ⅱ)center.These CoNOC-Tc-t porous carbon nanostructures have demonstrated prominent catalytic activities toward oxygen reduction reaction(ORR)in alkaline medium.Compared to the commercial Pt/C catalyst,the CoNOC-800-1(annealed at 800℃ for 1 hour)exhibits excellent catalytic activity via an efficient four-electron-dominant ORR process,as well as the superior durability and methanol tolerance,making it a cost-effective Pt-free ORR electrocatalyst.More importantly,the novel designed N-Co-O catalytic active sites are proposed and well demonstrated by experiments,which provides a promising approach to develop heteroatom-doped carbon-based electrocatalytic materials.