Diverse Metal-organic Frameworks Based On A Flexible Dithioether Spacer With Luminescence And Sensing Properties

MOFs are capable to be assembled by metal cations as nodes and organic ligands as linkers,through the interactions including coordination effects,van der Waals force,accumulation,hydrogen bonds and so on.MOFs is a class of promising sensing materials.The photoluminescence properties of MOFs rely on their structural features on a great degree,including organic ligands with conjugated?electrons,the coordination environment of metal central ions,permanent porosity and the interactions with guest molecules.The porosity of MOFs in principle can reversibly absorb and release the analyte,thus the sensor materials based on MOFs can be recycled and reused.Therefore,much efforts has proven to be that MOFs can be used as effective materials for detecting small molecules,for example cations,anions,organic vapor and explosives.To construct MOFs with desirable networks,the selection of appropriate ligands is much vital.In this work,we choose bis?4-pyridylthio?methane?4-bpytm?ligands which contain flexible backbones,-S-CH₂-S-spacers,which can give rise to diverse torsion angles between the two pyridyl nitrogen atoms.The flexibility and conformation freedom of 4-bpytm ligands are able to meet the coordination geometries of various metal ions to direct the tailored structures.Hence,SCS ligands are selected to bond different metal ions and three rigid ligands to construct fabulous arrangement frameworks.Herein,single-crystal X-ray diffraction analyses have been applied to determine these stuctures.Flexible 4-bpytm ligands bridging fumaric acid?fum?,terephthalic acid?bdc?,1,2,4,5-benzenetetracarboxylic acid?btec?generated the following seven metal organic frameworks:[M₂?4-bpytm??bdc?₂][M=Zn?1?,Cu?2?],[Cd?4-bpytm?₂?fum?₂]·3H₂O?3?,[Cd?4-bpytm??bdc?]?4?,[Zn?4-bpytm??bdc?]?5?,[Ni?4-bpytm??btec?_1/2]·5H₂O?6?,[Co₂?4-bpytm??btec?]·4H₂O?7?.3-6 possess different two-dimensional layer structures and 1,2,7 are 3D frameworks.3 and 5 features 4-connected 2-fold interpenetrated sql networks,4exhibits a six-connected hxl network based on dinuclear Cd clusters.6 is a uninodal three-connected hcb net.7 is a binodal?6,8?-connected network.1 and 2 are isostructural and showing 3-fold interpenetrated 6-connected pcu topologies based on bimetallic tetracarboxylate units.Particularly,the luminescence properties of 1 are investigated systematically.The results show that it is able to sense explosives or inorganic ions and could be applied as a luminescent sensor to detect 2,4,6-trinitrophenol?TNP?,nitrobenzene?NB?and Cu²⁺ions.