| Metal-Organic Frameworks(MOFs)are a class of highly ordered functional materials formed by the self-assembly of metal ions and organic ligands through coordination bonds.Because their structure and pore size can be designed and tuned,this kind of materials have considerable potential application in gas adsorption and separation,catalysis,fluorescence sensing,magnetism,and proton conduction so on.In this dissertation,a series of novel MOFs were synthesized by the reaction of three structurally related benzylamino tricarboxylic acid ligands with Zn2+and Cd2+salts.Their fluorescence sensing properties were fully investigated.The research mainly includes:1.FourZn/Cd-MOFs were synthesized based on 5-(3-carboxybenzylamino) isophthalic acid(H3L1) and 5-(4-carboxybenzylamino)isophthalic acid(H3L2),namely,[Cd(HL1)(bpea)0.5(H2O)]n(1),{[Zn(HL1)(bpe)]·2H2O}n(2),{[Zn(HL1)(bpea)]·H2O}n(3),and{[Zn(HL2)(bpe)]·DMF}n(4)(bpea=1,2-Di(4-pyridyl)ethane,bpe=1,2-bis(4-pyridyl)ethylene).Single crystal X-ray diffraction indicated that in complex 1 the dinuclear clusters{Cd2(CO2)4}were linked by carboxylic ligands to form a 1D chain structure,and the bpea ligands further connected these chains to form a resulting 3D framework.Topologically,the dinuclears could be viewed as 4-connected nodes and the point symbol was(65.8)with extended symbol of[6.6.6.6.62.82],typical of Cd SO4 net.Complexes 2-4possess two-dimensional layered structures.Complex 2 forms a 3D?3D interpenetration structure,complex 3 forms a 2D+2D?3D interpenetration structure and complex 4forms a 2D?2D interpenetrating structure.Fluorescence sensing properties showed that complexes 1-4 have fluorescence response to some trivalent metal ions and organic pollutant acetylacetone(acac).Complex 1 exhibited ratiometric luminescence sensing activities toward Al3+and Cr3+with turn-on effect.The luminescence color change can easily be distinguished with the naked eyes under UV-light irradiation.The complex can be use as a ratiometric sensor to detect Al3+and Cr3+.It can also detect Fe3+through turn-off mechanism.Significant enhancement difference was observed between Al3+and Cr3+by the competition experiments through mixing with Fe3+.Importantly,based on the special fluorescent properties of complex 1,we prepared a fluorescent test paper.It can realize the rapid and simple detection of the above ions,which extends its potential application in the biological and environmental areas.Complexes 2-4 exhibit enhanced fluorescence toward acac and quenching toward Fe3+.The study of fluorescence mechanism shows that Al3+with a high charge density and a smaller ion radius may interact easily with the–NH–groups within the MOF framework,which may enhance the luminescence of complex 1.The red shift observed in the fluorescence emission indicates strong exciplex formation between complexes 2-4 and acac,and the obvious enhancement should also be assigned to weak interactions between complexes 2-4 and acac.The competitive energy absorption between Fe3+and complexes may be mainly responsible for the luminescence quenching.2.Six Zn/Cd-MOFs were synthesized based on three ligands of 5-(3-carboxybenzylamino)isophthalic acid(H3L1),5-(4-carboxybenzylamino)isophthalic acid(H3L2)and 5-(3-carboxy-4-methoxybenzylamino)isophthalic acid(H3L3),namely,{[Zn(HL1)(bpy)]·H2O·DMF}n(5),{[Cd(HL1)(bpy)]4·8H2O·DMF}n(6),{[Cd(HL2)(bpy)]·3H2O·DMF}n(7),{[Cd(HL2)(bpea)·H2O]·H2O·DMF}n(8),{[Cd(HL3)(bpea)·H2O]·H2O·DMF}n(9)and{[Cd(HL3)(bpp)·H2O]·2H2O·DMF}n(10)(bpy=4,4-bipyridine,bpea=1,2-Di(4-pyridyl)ethane,bpp=1,3-bis(4-pyridyl)propane).Complexes 5 and 7 have similar three-dimensional structures containing dinuclear units{M2(CO2)4},which are further linked by carboxylic acid ligands to form a two-dimensional layered structure,and then linked by bpy auxiliary ligands to form a three-dimensional network structure.In complex 6,two Cd2+ions are linked by four carboxyl groups to form dinuclear units{Cd2(CO2)4},which are connected by carboxylate and bpy ligands to form 2D layers.The three-dimensional supramolecular structure is formed by the hydrogen bond O-H···O between the protonated carboxyl group of the ligand and the free water molecule and the?????stacking interaction of the benzene ring.Complex 8-10 demonstrate similar interpenetrating structures.Due to the flexibility of the carboxylic acid ligands,the part of the aromatic ring with the protonated carboxylate groups are located as dangling arms along the layers construncted by carboxylate ligands and N-containing ligands,in which the aromatic rings between adjacent layers are interpenetrated into the windows of the adjacent layers with face-to-face fashion.Consequently,interesting 2D?2D interdigitating and pseudo-threading frameworks are formed.Hydrogen bonding and benzene ring stacking interaction exist between the layers.The fluorescence measurement showed that complexes 5 and 7-9 have fluorescence enhancement effect on acetylacetone(acac)in DMF,and the lowest detection limit among these complexes is 0.58?M for complex 8.The five complexes all display excellent recognition properties for Cr2O72-by fluorescence quenching with the detection limit of complex 6 being 0.72?M,showing high sensitivity.Consequently,these materials can also be used as bifunctional fluorescent MOFs materials.3.Four low-dimensional Zn/Cd-MOFs were synthesized based on 5-(4-carboxybenzylamino)isophthalic acid(H3L2) and 5-(3-carboxy-4-methoxybenzylamino)isophthalic acid(H3L3)with transition metal salts and the chelating N-containing ligand dmbpy(5,5'-dimethyl-2,2'-bipyridine),namely,{[Zn(HL2)(dmbpy)]·H2O}n(11),{[Cd(HL2)(dmbpy)]·H2O}n(12),{[Zn2(HL3)2(dmbpy)2]·H2O·DMF}n(13),and{[Cd(HL3)(dmbpy)]·DMF}n(14).Due to the chelating effect of dmbpy ligands,all the four complexes have low dimensional structures.In complexes 11 and 12,the carboxylate ligands coordinate with the metal ions in the mode of(?1-?1)-(?1-?0)-(?0-?0)-?2 and(?1-?1)-(?0-?0)-(?1-?1)-?2 respectively,to form one-dimensional chains.In complex 13,two carboxyl groups of different phenyl rings connect adjacent metal ions to form a zero-dimensional dinuclear molecule,and a three-dimensional supramolecular structure is formed through intermolecular hydrogen bonds.The HL32-ligands in complex 14 are in the mode of(?1-?1)-(?1-?1)-(?0-?0)-?3 to link the Cd2+ions into dinuclear units{Cd2(CO2)4}.These dinuclear units are linked by two carboxyl groups on the same benzene ring to form 1D chains along the b axis.In addition to the difference of coordination mode,the dihedral angle between the two benzene rings in the ligands are between 50.8 and 107.8°,which fully shows the flexibility of-CH2-NH-group.Fluorescence measurements show that complex 11-14 can selectively and sensitively recognize Fe3+and Cr2O72-in DMF through fluorescence quenching,which indicates these complexes may have potential application in the field of fluorescence sensing.Our investigation further suggest that introduction of functional groups into the MOFs framework may represent a prospective strategy for designing the desired luminescent MOF/CP materials with high selectivity and sensitivity toward target pollutants. |
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