| Porous Coordination polymers(PCPs),a kind of emerging functional materials built from metal ions and various organic bridging ligands via self-assembly,has attracted intensive attentions due to their intriguing architectures as well as potential applications in the areas of gas sorption and purify,guest and ion's recognition and separation,catalysis and so on.Aromatic ligands containing cyano groups are considered as one of the most ideal candidcates for synthesies of novel microporous complexes with rigid channels due to their strong coordination abilities.On the other hand,it's shown that anion,solvent and synthesis methods play signficant roles in self-assembly of complexes.Herein we choose 1,4-bis(cyanomethyl)benzene(p-phda)and 1,4-dicyanobenzene(1,4-dcb)as organic ligands and AgX(X=CF3COO-or CF3SO3-)as anions to assemble three new complexes[Ag3(CF3COO)3(p-phda)1.5]n(1),{[Ag(p-phda)2](CF3SO3)}n(2)and{[Ag5(CF3COO)5(1,4-dcb)2]·2(C6H6)}n(3)in different solvents by different synthesis methods.Their crystal structures and thermal stabilities have been investigated by infrared spectra,elemental analysis,thermogravimetric analysis and X-ray crystallographic analysis.The ion exchange of complex 2 was investigated by infrared spectra and X-ray powder diffraction and the anion-induced photoluminescence was studied by fluorescence spectrum.For complex 3,its guest desorption,re-adsorption and selective adsorption properties were discussed by means of thermogravimetric analysis,NMR and X-ray powder diffraction.The main conclusions obtained in this paper are as follows:(1)Complex 1 is an unreported two-dimensional coordination polymer.It contains three crystallographically unique Ag(I)centers,which formed three-coordination Y-shaped trigonal planar and four-coordination distorted tetrahedron geometry respectively.Trifluoroacetate anion is coordinated in a syn-syn bidentate mode or tridentated mode to Ag centers,respectively.For comparison,1 and 1'({[Ag6(CF3COO)6(p-phda)2]·(C6H6)}n synthesized by our group)were prepared with same ligands,metal salts and the mol ratio but in different solvent while they have distinguished structure showing interesting solvent effect.(2)Single crystal 2 is a 2-D "fishing net" coordination polymer prepared by slow evaporation.The asymmetric unit of 2 contains only one crystallographically unique Ag(I)center.Ag is four-coordinated by four N atoms from four distinct p-phda ligands forming a distorted tetrahedron with N atoms as four vertices and Ag ions included inside.The most attractive structure feature of 2 is the CF3SO3- anion is not coordinated to Ag+ but as counter-ions filled in the cavity via hydrogen bonding interactions with the cationic framework.It's worth to note that CF3SO3-can be exchanged by different anions such as ClO4-,BF4-,PF6- and SCN" and the framework after ion exchanging remains essentially unchanged.In addition,the exchanged complex herein exhibits the anion-induced photoluminescence change.Complexes 1 and 2 possess distinct crystal structures due to using anions with different coordination abilities,showing the interesting anionic effect.Complex 2'((Ag4(CF3SO3)4(p-phda)2]n) that was obtained by diffusion method posses distinct structures from 2,showing the subtility of synthesis method.(3)Complex 3 forms 2-D sheets structure.The asymmetric unit contains three crystallographically unique Ag(I)centers and CF3COO- is participate in the coordination to form Y-shaped,three-coordinated trigonal planar and four-coordinated,distorted tetrahedron geometry,respectively.Benzenes are intercalated as guests in the channel formed between the sheets.The benzene guests can be desorbed and re-adsorbed with the expansion and shrinkage of the framework,demonstrating the reversible guest-induced host framework change.Furthermore,guest benzenes in 3 can be replaced by toluene and 3 shows a preferential adsorption of m-xylene over its ortho and para isomers,which may be applied in separation of xylene isomers. |
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