Assembly And Characterization Of Metal-Organic Coordination Polymers

Metal—organic coordination polymers are assembled from the organic ligands and one or more types of metal centers via coordination bonds.Studies on the coordination polymer materials especially the porous coordination polymer materials have been focused on due to their potential applications in selective separation,catalysis and gas storage.Lanthanide ions with flexible coordination geometries are excellent candidates for creating open frameworks by employing suitable space ligands.Researches on the coordination polymers have extended to the lanthanide-transition heterometallic polymers from the homometallic analogues with the development of supramolecular chemistry and coordination polymer crystal engineering.Two homometallic complexes have been hydrothermally obtained and characterized by single-crystal X-ray diffraction,thermogravimetric analysis and IR spectroscopy.Compound 1(Zn(HnicO)₂·(H₂O)₂,HnicO=2-hydroxynicotinic acid) with 3D supramolecular networks were constructed by[Zn(HnicO)₂·(H₂O)₂]building blocks via abundant dimeric(N-H…O) and cyclic tetrameric(O-H…O) hydrogen bonds.The unusually linear metal-water chain was comprised of tetrameric hydrogen bonds linked by zinc centers.Compound 2 ([Nd(H₂O)(HnicO)(TP)]·2H₂O,TP=terephthalate) possessed a 3D lanthanide-organic open framework with 1D channels containing lattice waters.This framework exhibited a high stability up to 330℃after removing lattice waters.The results show that lanthanide ions, which favor for constructing open frameworks with proper linear space ligands,have more flexible coordination geometries than transition metal ions.The conclusions can guide the further construction of open coordination frameworks with high stability.Compound 3(Ce₂(H₂O)₂(OAc)Cu₄Cl₃(IN)₆,HIN=isonicotinic acid,HOAc=acetic acid) was hydrothermally synthesized and characterized by single-crystal X-ray diffraction, thermogravimetric analysis,IR,UV-vis,photoluminescent spectroscopy.3D architecture of compound 3 was comprised of 1D Ce-carboxylate chains and {Cu₄Cl₃} complexes bridged by IN ligands.Compound 3 exhibited high stability analyzed by thermogravimetric experiment. Successfully constructing compound 3 proves the validity of the ligand-directed assembly strategy and provides more references for crystal engineering to the oriented design and synthesis of target products.