Synthesis, Structure, Gas Adsorption Of Metal-organic Frameworks Constructed From Multbentate Ligands

Usually, in the design and construction of metal-organic frameworks, introducefunctional groups through ligand modifications into pores and replace a vertex in anetwork by a clustered metal-ligands entity as a SBU are considered as two powerfuland effective synthetic ways. The former can efficiently tune gas adsorptionperformances, whereas the latter can provide an efficacious approach to constructMOFs with fascinating architectures and intriguing topologies.In the first part, two UiO-67analogues,[Zr6O4(OH)4(FDCA)6](BUT-10) and[Zr6O4(OH)4(DTDCA)6](BUT-11) with functionalized pore surfaces and highstability were synthesized from functional ligands9-fluorenone-2,7-dicarboxylic acid(H2FDCA) and dibenzo[b,d]thiophene-3,7-dicarboxylic acid5,5-dioxide (H2DTDCA),respectively, and structurally determined by single X-ray diffraction. Notwithstandingskeleton bend of the two ligands with respect to linear4,4’-biphenyldicarboxylic acid,which constructed UiO-67, the two MOFs have similar structures to that of UiO-67,with only lowered symmetry in their frameworks. Attributed to the additionalfunctional groups (carbonyl and sulphone, respectively) in the ligands, BUT-10and11showed enhanced CO2adsorption uptake and separation selectivities over N2andCH4, whereas decreased pore sizes and surface areas compared to UiO-67. At298Kand1atm, the CO2uptake is22.9,50.6, and53.5cc/g, and the infinite dilutionselectivities of CO2/CH4are2.7,5.1, and9.0, and of CO2/N2are9.4,18.6, and31.5for UiO-67, BUT-10and11, respectively. The selectivities of CO2/CH4and CO2/N2were thus enhanced1.9and3.3times for BUT-10and11compared with UiO-67,respectively. These results showed also that introducing carbonyl and sulphonegroups into pore surfaces of MOFs could significantly increase their affinity towards CO2molecules, thereby enhanced CO2capture ability, which provided a strategy forthe development of CO2capture materials. In addition, the adsorption and separationabilities of the two MOFs are quite high; they would thus be potentially applicable inCO2capture.In the second part, a fluorescent3D metal-organic framework with a two-foldinterpenetrated pcu topological structure was assembled by1,4-benzenedicarboxylicacid (H2bdc) with Zn ion by employing1,10-phenanthroline-5,6-dione (pad) acting asan assistant ligand. It is interesting that an unusual tetranuclar SBUZn4(μ3-OH)2(COO)6(N2)2was found in this structure. Firstly, two zinc atoms arebridged by three carboxylate groups, two N atoms and one μ3-OH to form a dinuclarZn2(μ3-OH)(COO)3(N2) SBU. Next, two dinuclar SBUs combine to form a tetranuclarZn4(μ3-OH)2(COO)6(N2)2SBU by sharing two μ3-OH. Finally, the obtainedtetranuclar SBUs are further connected by bdc ligands to form a three-dimensional(3D) framework.