Synthesis, Structure And Properties Of Metal-organic Frameworks Based On N-containing Ligands

The rational design and construction of metal-organic frameworks (MOFs) haveprovoked great interest due to their intriguing network topologies and potentialtechnological application such as gas adsorption and separation, catalysis, and thedevelopment of electronic, optical and magnetic materials. As we know, propertiesare inextricably linked with the natural structure. Therefore, the synthesis of targetMOFs with specific structure and exploration of novel structure are essential to studythe properties of MOFs. Moreover, the introduction of elaborate functional active sitesto the frameworks will lead to the improved functions of modified MOFs. Currently,nitrogen-containing ligands are widely used in the assemblies of MOFs and gasadsorption and separation because of their rich coordination modes and specialelectronic distribution. In this paper, we explore the effects of nitrogenous ligands onMOFs. The corresponding structural topologies and gas adsorption and separationproperties have been studied. The main contents are as follows:1. Through introducing the N-rich s-heptazine group in ligand design, an rht-typeMOF,[Cu3(TDPAH)(H2O)3]·13H2O·8DMA (Cu-TDPTH)(where TDPAH is2,5,8-tris-(3,5-dicarboxylphenylamino)-s-heptazine)(1) has been prepared. We reportthe storage capacities and separation selectivity of Cu-TDPAH for C2hydrocarbonsand CO2over CH4. Because Cu-TDPAH possesses the high concentration of openmetal sites and the highest Lewis basic sites density in rht-MOFs, this materialdisplays high C2H2/CH4selectivity of80.9as well as record high C2H6adsorption enthalpies (33.0kJ·mol-1). Theoretical calculations reveal that s-heptazine and NHgroups within the framework have synergistic effects on CO2binding.2. We report the storage capacities and separation selectivity of an rht-type MOF,Cu-TDPAT (TDPAT=2,4,6-tris(3,5-dicarboxylphenyl-amino)-1,3,5-triazine)(2), forC2hydrocarbons over CH4. Henry’s constant, isosteric heat of adsorption (Qst), andIAST selectivity are calculated based on single component sorption isotherms.Theoretical calculations indicate that both open metal sites and Lewis basic sites havestrong interactions with C2molecules. The combination of these two kinds of sitesleads to the highest C2H2/CH4selectivity of127.1as well as record high C2H4adsorption enthalpies (49.5kJ·mol-1). To mimic real world conditions, breakthroughexperiments are conducted on equimolar four-component mixture containing C2H2,C2H4, C2H6, and CH4at room temperature and1atmosphere. The findings show thatCu-TDPAT is a promising candidate for CH4capture and purification.3. A large size semi-rigid polytopic N-containing ligand H2atpia[H2atpia=5-(3-amino-tetrazole-5-phenoxy)-isophthalic acid] has been successfullyprepared. By the reaction of H2atpia with transition metals, three MOFs, namely[Cd(atpia)]2(3),[Cu3O2(atpia)2](4), and [Mn3(OH)2(atpia)3]·1.25H2O (5) have beensynthesized. These three compounds all display new topologies. Compound3exhibitsa3D (2,3,10)-connected framework with (4·62)2(412·618·811·104)(4)2topology.Compound4possesses a2D3-nodal layer with (416·614·811·104)(43)2(4)2topology.Compound5features a2D (3,3,8,8)-connected structure with unprecedented(3·42)2(34·46·56·68·73·8) topology. The diverse structures of these three compoundsdemonstrate that the distinctive coordination modes of different metals have asignificant impact on the construction of MOFs. Moreover, the photoluminescenceand magnetic properties have been studied and discussed.4. Two cadmium-organic frameworks were synthesized under solvothermalcondition, namely,[Cd(dptz)2]·{Cd[(NH2)2CS]4}·(NO3)4(6) and Cd(dpmtz)2(7)dptz=3,6-di-(pyridin-4-yl)-1,2,4,5-tetrazine,dpmtz=3,6-di-(pyridin-4-yl)-1,2-dihydro-1-mercapto-1,2,4,5-tetrazine). The layers in6form a3D porous MOF withinterlocked structure via inclined interpenetration. Compound7was prepared through an in situ ligand reaction in which generated a new ligand dpmtz and the frameworkbelongs to a3D net with dia type. The adsorption behavior shows that compound7has selective adsorption capacities of CO2over N2...