Syntheses,Structures And Properties Of Two-Dimensional Zinc/Cadmium Coordination Polymers

As a new class of porous material,coordination polymers?CPs?possessing large surface area,high porosity,and variable topological characteristics,have become the current research hotpot in the field of materials science and chemistry,for their potential applications in gas adsorption and separation,catalysis,magnetism,and drugs release,chemical sensing and other aspects.In particular,the luminescent CPs has attracted widespread attention due to they not only show the variability of fluorescence performance,but also possess high selectivity,sensitivity and strong anti-interference ability in chemical sensing.During the synthesis of CPs,the changes of metal centers and minor differences in the ligands of symmetry,substituent groups,and sizes can bring about various structure of CPs,which in turn affects their fluorescence properties.Therefore,it is still a challenge to design luminescent CPs rationally with predictable structures and adjustable channels.In this paper,we select Zn²⁺or Cd²⁺in the d¹⁰ configuration as the transition metal centers,and large size of nitrogen-containing polycarboxylic acid as the bridging ligands to construct new luminescent CPs under different solvothermal conditions,and the effects of synthesis condition on the structure and luminescence property of CPs were studied.In addition,we explore the applications of luminescent CPs in fluorescence modulation and sensing metal ions,small organic solvent molecules,nitro explosives and other aspects to provide a research basis for the design,synthesis and application of new type of luminescent CPs.The main research results are as follows:1.UsingaflexibleN-containingtricarboxylicacidligand5-[?3-?4-carboxyphenyl?-1H-pyrazol-1-yl?methyl]isophthalic acid?H₃L?and Zn?NO₃?₂·6H₂O metal ions,an anionic coordination polymer has been prepared solvothermally,[Zn?L??H₂O?]·?Me₂NH₂?·DMF?1?,?DMF is equivalent to N,N'-dimethylformamide?.1 is a two-dimensional layered structure,in which the?Me₂NH₂?⁺cations are located.1 possesses high stability in different organic solvents and exhibits excellent fluorescence sensing properties for Fe³⁺,Cr₂O₇^2-,and aromatic nitro compounds with high sensitivity and selectivity,respectively.Since 1 possess anionic framework,lanthanide ions(Eu³⁺,Tb³⁺)were encapsulated into the pores of 1by cation-exchange,and realized tunable luminescence and white-light emission by adjusting different molar ratios of Eu³⁺and Tb³⁺ions and changing the excitation wavelength.Moreover,Tb³⁺@1 is capable of detecting the organic solvent small molecule acetone by fluorescence quenching.2.Using 4,4'-bipytidne?4,4'-bipy?and terephthalic acid?H₂bdc?as auxiliary ligands,three layered Cd-CPs,CdL?H₂O?]·2H₂O?2?,[CdL?H₂O??4,4'-bipy?0.5]·H₂O?3?and[CdL?H₂O?₂]·0.5H₂bdc?4?were synthesized by self-assembly of 5-?4-pyridine?methoxym-phthalic acid?H₂L?and Cd?NO₃?₂·6H₂O under solvohermal conditions.Further study showed CPs 2-4 can be quickly synthesized by microwave-assisted solvothermal synthesis?MWAS?method.Compared with conventional solvothermal synthesis method,MWAS not only greatly decreases reaction time but also and reduces the size of product.In compound 2,two adjacent Cd²⁺are bridged with carboxyl groups by the coordination mode of bidentate chelation to form a binuclear[Cd₂N₂O₁₀]secondary structural primitive,which is connected by L^2-ligand to form a2D layered structure with quadrangle windows.In compound 3,Cd²⁺connects with L^2-ligands to form an infinitely extended 2D monolayer sheet structure,and then the4,4'-bipy link the adjacent sheets to form an interesting two fold interpenetrated structure with rhombic windows.In the structure of 4,the Cd²⁺ions links with L^2-ligands to form a 2D layer and uncoordinated H₂bdc ligands are penetrated into the rhombic windows of the adjacent layers.Compound 2-4 exhibit good fluorescence sensing properties for selectively sensing Fe³⁺ions in aqueous solution with high sensitivity and selectivity as well as strong anti-interference sensing ability,and their uminescence quenching mechanism has been discussed in detail.In addition,compound 3 can adsorb organic dyes effectively in water,indicating it may be used as a potential dye adsorbent.