Proton Conductivity And Adsorption Properties Of Metal Organic Framework Materials Based On Carboxyphosphonates Ligands

Metal-organic frameworks(MOFs)or coordination polymers(CPs)have become one of the fastest growing fields in the chemical field due to their structural and functional tunability.In the past two decades,the application fields of MOFs have been expanding.Metal phosphonates are an important class of CPs or MOFs.The versatile coordination modes and strong coordination capabilities of the phosphonate ligands result in a number of metal phosphonates with abundant structural types and interesting properties.Introducing additional organic functional groups into phosphonate ligands can not only obtain compounds with novel structure but also interesting properties.However,due to the crystallization is often quite difficult and the easy formation of a layered structure,the correlation between metal phosphonates structure and the proton conductivity is not clear enough,and there are few studies on gas adsorption.In this thesis,we selected carboxyphosphonates bifunctional ligands to construct a series of CPs materials,and studied their proton conductivity and gas adsorption properties according to their structural characteristics.Although proton conductive metal phosphonates with well-defined structure offer a favorable platform for exploring their structure-property relationship,to investigate synergic effect of phosphonate groups and functional moieties on proton conduction is rare.In this work,we have synthesized two new copper phosphonates[Cu(4-cpp H)(4,4?-bipy)(H₂O)₃](FJU-80)and[Cu(4-cpp H)(4,4?-bipy)]·H₂O·DMF(FJU-81)by the method of solvent-assisted modification,giving a 1D metal coordination polymer and a 3D metal open-framework,respectively.Single-crystal X-ray diffraction(SCXRD)shows that FJU-80 is full of hydrogen-bonding sites contributed from improved synergic effect of phosphonate groups,carboxylate groups and coordinated waters,thereby facilitating continuous hydrogen bonding networks,whereas FJU-81 only has discrete hydrogen bonding fragments.Powder X-ray diffraction(PXRD)and impedance analyses confirm that FJU-80 possesses higher water stability as well as improved proton conductivity,indicating that solvent-assisted modification is effective to increase the hydrogen-binding sites from phosphonate groups and functional moieties,and then to realize facile proton transfer.To date,three methods have been used to tune the proton conductivity of MOFs.The first was to change the acidity of the functional groups on frameworks by chemical modification.The second was to introduce proton conducting chemicals(imidazole molecules and H₃PO₄).The third was to control the amount of conducting media(water or methanol).For controlling the amount of conductive media,the external stimulus of atmospheric components is generally used to dynamically change the proton conductivity.However,there are few studies on how to effectively control the number of guest molecules through the regulation of the structure.By changing the length of the ligand,we obtained two cases of isoreticular MOFs,FJU-81 and FJU-810.The proton conductivity of MOFs is adjusted by increasing the length of the ligand and increasing the content of lattice water in the pore channel.FJU-810 with high lattice water content exhibits higher proton conductivity than FJU-81 with low lattice water content.At 80°C and 98%humidity,the conductivity of FJU-810 is about 375 times higher than that of FJU-81.This study shows that rational design of the length of the ligand can effectively regulate the proton conductivity of MOFs.It is highly necessary to develop new strategies for energy-efficient separation of C₂H₂ from CO₂.Porous material-based adsorptive separation is considered to be a promising future separation technology with more environment friendly and energy efficient when compared with cryogenic distillation or organic solvent extraction.Among all kinds of solid porous materials,MOFs materials are considered to be the most promising candidates for such an application.The rational design and construction of MOFs with complex structures is prime important in reticulation chemistry.Some researchers have introduced a systematic design principle,named the merged net strategy,targeting the design of highly complex mixed-linker MOFs.Based on the structural characteristics of the merged net,FJU-812 with a new topology was synthesized via solvothermal reaction of H₄L as the 3-c MBB,1,2-bis(4-pyridyl)ethylene as the 2-c MBB,and Cu(NO₃)₂·3H₂O.FJU-812 is a new type of MOFs based on a 10-c tetranuclear Cu(II)MBB,a 3-c MBB and a 2-c MBB.The grid structure can be an assembly of spn net and hxg net,and named as the sps net.FJU-812 shows permanent porosity accompanied with hierarchical pores and superior gas selective adsorption performance.In addition,FJU-812 can efficiently trap C₂H₂ from C₂H₂/CO₂ and C₂H₂/CH₄ mixture gases through fixed-bed dynamic breakthrough experiments.