Luminescence Sensing Activities And Magnetic Properties Of MOFs Crystalline Materials Based On Phenoxycarboxylic Acids

Metal-Organic Frameworks（MOFs）are porous materials with designable structures,controllable functional sites,and limited pores,which have considerable application prospects in gas adsorption and separation,catalysis,fluorescence sensing,biomedicine,magnetism,and light control.Reasonable selection of metal centers and organic ligands is crucial to the synthesis of MOFs,which have become a research hotspot of chemical researchers in recent years.In this dissertation,three isomeric flexible tricarboxylic acid ligands with ortho-,para-and meta-substituted phenolic groups were selected as the organic building units.Based on these ligands,a series of MOFs with novel structures were synthesized.Their emission regulation,fluorescence sensing and magnetic properties were studied.The research mainly includes:1.Four lanthanide-based MOFs（LnMOFs）have been synthesized based on ortho-phenolic carboxylic acid ligand 2-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L1）and para-phenolic carboxylic acid ligand 4-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L2）,namely,[Ln（L1）（DMF）（H₂O）]_n（Ln=1 Eu 2 Tb）,{[Ln（L2）（DMF）₂]·H₂O·0.5DMF}_n（Ln=3 Eu 4 Tb）.Complex 1-2 are isostructural.Dimer units Eu₂（μ-CO₂）₂（η-CO₂）₂ are formed by the connection of carboxylate groups.Each dimer unit is further connected to six other neighboring ones through L1^3-ligands,extending into a 3D network.From the topological view,the dimer units can be abstracted as 6-connected nodes,while the L1^3-anions can be signified as 3-connected nodes,respectively.Consequently,the topology is represented as（3,6）-connected（4.6²）₂(4².6¹⁰.8³),typical of rtl net.Complexes 3-4 are isostructural.The neighboring Eu³⁺ions were bridged through oxygen atoms from the carboxylate groups of branched organic ligand,forming the[Eu₂（COO）₆]_n secondary building unit（SUBs）.The neighboring dinuclear[Eu₂（COO）₆]_n units were connected to form 1D chains.The adjacent1D chains were linked by the carboxylate groups further to generate 2D layer.The adjacent2D layers further accumulate into a 3D framework.From a topological point of view,dinuclear[Eu₂（COO）₆]_n SBUs and H₃L2 ligands can be considered as 6-and 3-connented nodes,respectively.As a result,the framework can be viewed a 3,6-connected{4²·6}₂{4⁴·6²·8⁷·10²}topology.Upon excited at 398 nm,complexes 1 and 3 exhibit characteristic ⁵D₀→⁷F_J（J=1-4）transition emission peaks of Eu³⁺ions,which corresponds to red region emission.When excited at 325 nm,complexes 2 and 4 exhibited transitions of four characteristic emission peaks（⁵D₄→⁷F_J,J=6,5,4,and 3）of Tb³⁺ions,corresponding to green region emission.By adjusting the ratio of Eu/Tb,two series of doped complexes,1-Eu_xTb_1-x and 2-Eu_xTb_1-x,were obtained.Solid-state fluorescence tests showed that with the increase of Tb³⁺content,the decrease of characteristic peaks of Eu³⁺ion is not obvious.For 1-Eu_xTb_1-x MOFs,the blue emission intensity from the ligand H₃L1 shows gradual increase with the increase of Tb³⁺content.Consequently,the mixed colors of red(Eu³⁺ion),green(Tb³⁺ion)and blue（H₃L1 ligand）could provide potential white emission.It is worthy to note that the CIE coordinate of point（Eu/Tb=6:4）and（Eu/Tb=7:3）is（0.3385,0.2462）and（0.3136,0.2563）,respectively,close to that of typical white light materials with CIE coordinate of（0.333,0.333）.For 2-Eu_xTb_1-x MOFs,the influence on H₃L2ligand decreases compared with H₃L1 in 1-Eu_xTb_1-x.These results indicate that two series of doped complexes showed the potential value of white light emission.In addition,these four complexes can be as excellent selective and sensitive luminescent sensors towards Fe³⁺,Cr₂O₇^2-and CrO₄^2-in aqueous media.Fluorescence mechanism studies showed that the quenching effect of Fe³⁺,Cr₂O₇^2-and CrO₄^2-should be assigned as the synergetic effect of inner filter effect and weak interactions between MOFs and analytes.2.Seven MOFs have been synthesized based on three isomeric phenolic polycarboxylic acid ligands,2-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L1）,4-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L2）and 3-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L3）with different nitrogen-containing ligands and transition metals,namely,{[Cd_1.5（L1）（4,4’-bpy）（H₂O）]·DMF·2H₂O}_n（5）,[Zn（HL2）（4,4’-bpy）（H₂O）]_n（6）,{[Zn₂（HL2）₂（Ls）（H₂O）]?3H₂O}_n（7）,{[Zn（HL3）（bpea）]?DMF}_n（8）,{[Cd_1.5（L3）（bpea）_1.5（H₂O）_1.5]?0.5H₂O}_n（9）,{[Ni（HL1）（bpe）（H₂O）]·0.5DMF·0.5H₂O}_n（10）,{[Ni（HL1）（bpe）_1.5（H₂O）]·DMF·3H₂O}_n（11）,{[Co_1.5（L1）（4,4’-bpy）_1.5]·DMF·2H₂O}_n（12）,{[Co（HL3）（bpea）]?DMF}_n（13）（bpea=1,2-di（pyridyl）ethane,4,4’-bpy=4,4’-bipyridine,Ls=2,5-bis（4-pyridyl）-1,3,4-thiadiazole,bpe=1.2-bis（pyridin-4-yl）ethene）.Complexes 5 and 12 have similar 3D structures.In these complexes,the secondary structural unit（SBU）of Cd₂（CO₂）₄ is formed between two adjacent Cd1 atoms.The carboxylic acid ligands act as bridges in the middle of adjacent secondary structures to form a 1D carboxylic acid chain structure.The 2D layered structure is formed between the chains by the carboxylic acid ligand on the ac plane.Cd1 is distributed above and below the 2D layer under the linkage of carboxylic acid ligands.In addition,the bpy ligand linked these 2Dlayers to generate a 3D structure.In complex 6,the two metal centers formed a secondary structural unit Zn₂（CO₂）₄.The ligand HL2^2-connected the secondary units into a1D chain structure.A 3D supramolecular structure is formed under the action of hydrogen bonds.In complex 7,the central Zn metals are connected by ligand Ls into binuclear units,which are connected by the carboxylic acid group derived from the same benzene ring into a 1D chain structure.The carboxyl group on the other benzene ring does not participate in the coordination.Complex 8 and 13 are isostructural.In the structures,different metal atoms are linked by the carboxylic acid ligands to form 1D chains along the c-axis.The bpea ligands also connected metal atoms along the b-axis to form 1D chains.By sharing the metal centers,two kinds of chains are linked to form 2D layer along the bc plane.The resulting 3D self-intercalation structure is formed throughπ???πstacking interactions between adjacent benzene rings.In complex 9,the Cd1 atom in the adjacent dinuclear unit shares half Cd2 atom due to the existence of the disordered structure.Further,the adjacent dinuclear unit forms the secondary structural unit Cd_2.5（CO₂）₆.The secondary building blocks are conencted across carboxylic acid ligands to form a 1D chain.The carboxyl groups from other benzene rings linked these chains to form 2D metal-carboxylic layer.Bpy ligands connect these layers into the resulting 3D structure.In complex 10,the partly deprotonated carboxylate ligands connect Ni^II centers,forming 1D linear chains along a axis.These chains were further linked by bpe ligands,extending into 2D layers along the ab plane with HL1^2-ligands as detangling sides arranged above and below the layer alternatively.Adjacent layers are stacked together through interactions between the aromatic rings,forming a 3D supermolecular structure.In complex 11,the carboxylate ligands connect Ni^II centers,forming 1D S-shaped chains along a axis.Bpe ligands connect Ni^II centers to form a 2D layer in this case.Special hexagonal cavities are formed with six Ni^II centers at the corner and six bpe ligands at the edge around each Ni₆（bpe）₆metallmacrocycle.The adjacent layers form novel inclined interpenetration between two groups of interpenetrating layers.The final 3D structure is formed by the connection of these inclined interpenetrating layers and the carboxylate chains through sharing the metal centers.Further TOPOS analysis reveals that the framework is a rare uninodal 5-connected network with a point symbol of（4⁴?6⁶）.Fluorescence measurements showed that complexes 5-9 showed excellent recognition properties for Fe³⁺,Cr₂O₇^2-and CrO₄^2-in H₂O.In addition,complexes 8 and 9 also can be excellent luminescent sensor for Cr³⁺.Complexes 10 and 11 which were produced in the same reaction system demonstrate interesting crystal-to-crystal transformation by adjusting the ratio of the reaction raw materials and the reaction time.Magnetic tests indicate that antiferromagnetic interactions exist between the Co²⁺ions in complexes 12 and 13.3.Three LnMOFs have been synthesized based on 2-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L1）,4-（3,5-dicarboxybenzyloxy）benzoic acid（H₃L2）,namely,[Ln（L1）（H₂O）（DMF）]_n（Ln=Sm 14,Gd 15,Dy 16,Ho 17,Er 18,Y 19）,{[Gd（L2）（DMF）₂]·H₂O·0.5DMF}_n（20）.Complexes 14-19 and complex 1-2 are isostructural.Complex 20 and complex 3-4 are also isostructural.The magnetic measurments show that antiferromagnetic interactions were observed between adjacent metal centers within complexes 15,16 and 20.In this dissertation,20 kinds of MOFs were synthesized assembled from three isomeric phenolic polycarboxylic acid ligands,which demonstrate excellent luminescence sensing and magnetic properties.Our research shows that organic building units play an important role in regulating the structure and function of MOFs.