New Cd²⁺,Co²⁺ And Zn²⁺ Coordination Polymers Co-modified By Halogen/Pseudohalogen And Imidazole/Triazole Derivatives:Syntheses,Structures And Properties

As an important branch of the hybrid organic-inorganic materials,the design and synthesis of novel thiocyanatocadmates have attracted a certain attention due to their structural diversity,and the potential applications in optics and pollutant degradation.Over the last three decades,by employing various substances to act as the countercations,the researchers have constructed many novel thiocyanatocadmates.So far,the reasonthat people’s study enthusiasm to this direction has not been cut is thatthe structures of the as-synthesized halometallatesare still unpredictable when a new organic ligand isused.Hybrid self-assembly process is pretty complicated,and many factors affect on the the final structure of the compound,such as the geometry ofthe metal ion,the coordination mode of the halide or pseudohalide ion,the form,size and charge of the organic base,aswell as the detailed experimental conditions.Our research group is now working on the synthesis of novel and excellent cadmium thiocyanate compounds,and to explore the effects of these factors on the structure and properties of cadmium thiocyanate.In this paper,through the direct method,three compounds were obtained with imidazoles and triazole derivatives as the ligand at room temperature,namely as[H₂（L1）][Cd₂（SCN）₆]（1）,[H₂（L2）][CdI₂（SCN）₂]·H₂O（2）,[CdCl（SCN）（L3）]（3）.In addition,we selected L4 serving as countercation to react with Cd²⁺and obtained two compounds,[H₂（L4）][CdCl₄]（4）and[H₂（L4）]₂[CdCl₄（SCN）₂]（5）,respectively.Finally,two compounds were synthesized by the other M²⁺and X^-,namely[Co（SCN）₂（L5）₂]（6）and[Zn（N₃）₂（L6）]（7）.By the X-ray single crystal diffraction test and the SHELXTL-9 software,we get the precise structure of the seven compounds,and discuss the properties of these compounds through XRD,IR,UV and PL,element analysis and TG.The main results of this paper are as follows:1.At pH=2,the simple room-temperature self-assemblies between Cd²⁺salts,SCN^-and organic bases created three new thiocyanatocadmates as[H₂（L1）][Cd₂（SCN）₆]（L1=1,4-bis（2-methyl-1H-imidazol-1-ylmethyl）benzene）（1）,and two new halo-thiocyanatocadmates as[H₂（L2）][Cd I₂（SCN）₂]·H₂O（L2=3,5-bis（4-pyridyl）-1,2,4-triazole）（2）,and[CdCl（SCN）（L3）]（L3=3-pyrazinyl-1,2,4-triazole）（3）.In 2 and 3,X^-（X=I for 2,Cl for 3）appear in the final structures.X-ray single-crystal diffraction analysis reveals that（i）in 1,with H₂（L1）²⁺as the countercation,the SCN^-groups tri-bridge the Cd²⁺centers into a 1-D chained thiocyanatocadmate;（ii）2 is only a mononuclear iodo-thiocyanatocadmate,and[H₂（L2）]²⁺acts as the countercation.But via thep···pand N_pyridyl-H···N_SCNCN interactions,H₂（L2）²⁺and[CdI₂（SCN）₂]^2-aggregate together to form a 1-D supramolecular tube.Amongst the tubes,a chained water cluster with a zig-zag shape is observed;（iii）3 is an organically extended chloro-thiocyanatocadmate.Note that the report on this type of material is rather rare.It possesses a 3-D network with a dia topology,in which a castellated CdCl⁺single chain is observed.The photoluminescence spectra show that 1-3 all emit light（green light for 1,blue light for 2 and 3）,which should be attributed to the ligand-centered electronic transfer.Finally,the photoluminescence property of 3 were studied,and it was found that 3could detect NB.Due to the existence of SCN^-in 1-3,they can be used to detect the concentration of Fe³⁺by the colorimetric method simply.2.In order to explore the effect of the mixed SCN^-on the structure and property of halocadmates,two compounds were obtained using L4 to react with Cd²⁺,SCN^-and Cl^-through direct method at room temperature,namely[H₂（L4）][CdCl₄]（4）and[H₂（L4）]₂[CdCl₂（SCN）₄]（5）.X-ray single crystal diffraction test showed that（1）4 is a 1-D Cd-chlorate.In 4,Cd²⁺and Cl^-first self-assembly to form a binuclear cluster[Cd₂Cl₈]^2-,then the[Cd₂Cl₈]^2-form into a 1-D chain with H₂（L4）²⁺acting as a linker under N-H···Cl hydrogen bond;（2）5 is a 0-D chloro-thiocyanatocadmat.After the introduction of SCN^-,the Cl^-in CdCl₂ is partially replaced and appears in the final structure of 5.Unlike 4,Cl^-in 5 is only a terminal ligand.The photoluminescence aspectra shows that 4-5 both have good photoluminescence properties,and 5 was significantly weaker than that of 4,which was probably caused by electron transfer in the excited state molecule（ESIPT）or hybrid.4 has a good thermal stability compared with 5.5 can detect the concentration of Fe³⁺by colorimetric method.3.By solvothermal method,one new compound was obtained after changing metal ions to Co²⁺,which is[Co（SCN）₂（L5）₂]（L5=1,4-bis（triazol-1-yl）benzene）（6）.Then modified by N₃^-,[Zn（N₃）₂（L6）]（L6=1,4-bis（triazol-1-ylmethyl）benzene）（7）was obtained through the hydrothermal method.6 is a 2-D layered cobalt-thiocyanate complexes with L6 coordinated.7 is a 1-D chained structure formed by the Zn²⁺,N₃^-and L6.Although MCl₂（M=Cd,Zn）is used as the M²⁺source,the Cl^-does not appear in the structures of 6-7.7 emits blue-violet light,which can be attributed to the ligand-centered electronic excitations.TG curves show that 6 has a good thermal stability,and it begins to break down when the temperature reaches 320oC.7 can act as chemical sensor to detect NB and Fe³⁺.