| Metal-organic frameworks?MOFs?are a class of porous crystal materials with high specific surface area and adjustable pore size.Tuning the kinds of ligands or metal salts can make MOFs have various crystal structures and properties,which can apply to the gas adsorption and separation,sensing,catalysis,drug delivery,magnetic materials and so on.Comparing to other porous materials?eg,zeolite or carbon materials?,MOFs can modulate the chemical properties of the pore surface by altering the groups in the organic linker.Here in,we chose a trinuclear iron cluster connected by?3-O as metal source.By changing the ligands?replacement of C2 symmetric rigid carboxylate ligand with C3symmetric rigid carboxylate ligand?,temperature,the solvents and pH,five novel Fe-MOFs are successfully prepared,which realized the transition from single secondary building units?SBUs?to double SBUs.The structure,stability,gas adsorption performance and magnetic properties of these compounds are studied systematically.The specific research contents are as follows:?1?Under solvothermal conditions,using a pre-synthesized trinuclear iron cluster Fe3??3-O?as a metal source and C2 symmetric rigid carboxylate ligand,4,4'-diphenyl phthalate?4,4'-H2bpdc?and 1,4-terephthalic acid?H2BDC?,respectively,two novel three-dimensional?3D?microporousFe-MOFscontainingsingleSBUs,[Fe3III??3-O??4,4'-bpdc?3?DMA??H2O?2?CH3COO?3DMA?CH3CN]n?1?,[FeIII?BDC??H2O?2?COOH?H2O]n?2?,havebeenobtained.Incompound1,[Fe3??3-O??CO2?6?DMA??H2O?2]SBU is bridged by 4,4'-bpdc2-ligands to form 3D network with 19.18×14.64?2 pore channels.Compound 1 shows a unique structure of double interpenetration that interspersed in different directions,exhibiting excellent chemical stability.The N2 adsorption test shows that compound 1 exhibits a reversible type-I adsorption isotherm model,which verifies that compound 1 has a microporous structure with a BET surface area of 1638 m2 g-1,and its N2 adsorption capacity is 661 cm3 g-1 at 1 bar and 77 K.In compound 2,the mononuclear Fe atoms are bridged by the co-ligand H2O molecules to form1D chain SBUs,and then these SBUs are further connected by the BDC2-ligands to form a3D network with a rhombic channel.Compound 2 shows a topological type of pcu and has good thermal and chemical stability.?2?On the basis of the above work,using C3 3-connected 1,3,5-tristricarboxylic acid?H3TMA?rigid ligand instead of the C2 2-connected ligand,and changing the solvent and the pH value,three 3D microporous Fe-MOFs[Fe2II?TMA?2?H2O??[?CH3?2NH2]2]n?3?,[Fe5II?TMA?3?CH3COO?2?DMF?2?[?CH3?2NH2]?DMF?H2O]n?4?,and[Fe7IIFeIII?OH?4?TMA?5?H2O?2[?CH3?2NH2]2?4DMF]n?5?with two different SBUs were obtained.The classic paddle-wheel like dinuclear Fe2-SBU and mononuclear iron SBU are bridged by TMA3-ligand to form compound 3 with 3D porous network structure.The rod-shaped dinuclear Fe-clusters are bridged by CH3COO-ion to form the unique 1D sinusoidal-like chain SBU,and then further connected to the paddle-wheel like Fe2-SBU through the TMA3-linker to form the 3D structure of compound 4,showing an excellent stability.While in compound 5,the Fe3-cluster bridged by?3-OH-are further bridged by the carboxylate groups of the TMA3-linker,forming a disc-shaped Fe7-SBU,and then the TMA3-linkers connect the Fe7-SBU to the mononuclear iron SBU to form a 3D stable network with two different channels.Gas adsorption tests confirmed compounds 4 and 5 are microporous structures.Magnetic studies indicate that antiferromagnetic coupling is present in compounds4 and 5. |
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