Vapor Adsorption Properties Of Flexible Coordination Polymers Based On Heterocyclic Carboxylic Acid

Flexible porous coordination polymers(FPCPs)have become a research hotspot in the field of gas storage and separation due to their dynamic structural transformation characteristics.Heterocyclic carboxylic ligands occupy a large proportion in the construction of coordination polymers.On the one hand,oxygen atoms in carboxylic acid have strong coordination ability and various coordination modes with metal ions,the gegerated coordinated compounds have high porosity and large pore size;On the other hand,the nitrogen and sulfur atoms in the heterocyclic ligand exhibit highly active,which is beneficial to the adsorption and separation properties of the complex.Therefore,flexible coordination polymers with different structures and their vapor adsorption properties were studied in this thesis,the main results are as follows:(1)A 1D flexible coordination polymer[Zn(3-tba)₂]·DMA(1?,DMA=N,N'-dimethylacetamide)was synthesized under solvothermal conditions by using a"V"-type triazole-carboxylic acid ligand 3-Htba(3-Htba=3-(4H-1,2,4-triazol-4-yl)benzoic acid.).Compound 1?experiences two-step single-crystal to single-crystal transformations(1??1??2).Firstly,1?transforms a nonporous one-dimensional crystal after the removal of DMA molecules,and then into a discrete binuclear complex2 upon exposure to water vapor.This two-step SCSC process are reversible.1?shows a gate-opening effect and high water uptakes(about 133.3 cm~3/g at 298 K).In addition,it shows selective water adsorption over alcohol,and the selectivity for water adsorpiton in the mixture of water/methanol is higher than that of 3A molecular sieve under vapor conditions.(2)Vapor adsorption properties of flexible coordination polymer[Zn₂(DMTDC)₂(bpe)](3?,H₂DMTDC=3,4-dimethylthieno[2,3-b]thiophehe-2,5-dicarboxylic acid,bpe=1,2-di(pyridin-4-yl)ethane)were studied.Vapor adsorption tests show that 3?has a high capacity of benzene(91.4 cm~3/g)adsorption,and only a little uptake for cyclohexane(6.1 cm~3/g).Gas chromatography reveals that 3?has a high benzene selectivity(96.64%)in the equal molar mixture of benzene and cyclohexane.The 3?@C₆H₆can return to 3?by heating,3?remains the similar uptake after six cycles of benzene adsorption.(3)A new 3D porous flexible coordination polymer[Zn₂(DMTDC)₂(dpbz)]·5DMF·0.5H₂O(4?,dpbz=1,4-di(pyridine-4-yl)benzene)was synthesized under solvothermal conditions.By removing guest molecules,the[Zn₂(DMTDC)₂(dpbz)](4?)was obtained,and displays a smaller pore size.Gas adsorption of N₂(77 K)and CO₂(195 K)for 4?exhibit multi-step adsorption behaviors,which are characteristic features of flexible coordination polymers.Vapor adsorption tests indicate 4?has a selective adsorption for benzene vapors(91.4 cm~3/g)over cyclohexane(5.2 cm~3/g).The separation of benzene and cyclohexane mixtures was investigated by using 4?as a stationary phase filled capillary column.The results showe that 4?-based chromatographic column completes baseline separation of the mixture of benzene and cyclohexane,and have a good reproducibility.