Syntheses And Characterization Of Series F Metal-Organic Frameworks Onstructed From Polycarboxylic Acids

Investigations of the assembly of metal-organic frameworks (MOFs)based on the lanthanide family have become the robust subject of manycurrent studies due to not only their versatile architecture, but also theirpotential applications as gas storage, selective gas absorption andseparation, catalysts, magnetic and luminescent materials. Polycarboxylicacids are the "star ligands" in coordination chemistry of such MOFs at alltimes because of (a) the inherent negative charge of carboxylate groupscompensate for the charge induced by metal cations and can mitigate thecounterion effect;(b) the diverse coordination modes provide thepotential for the formation of metal-organic bridging units, which helpenhance the robustness of the resulting network architectures. Thelanthanide ions have novel4f outermost layer electrons and largecoordination numbers, and the MOFs constructed from lanthanide ionspresent excellent optical, electronic and magnetic properties. In addition,the lanthanide ions prefer to coordinate with oxygen atoms frompolycarboxylic acid ligands to form stable Ln-O bonds. And the MOFsbased on Ag(I) attract many researchers' interests due to its versatilecoordination environments and diversied coordination numbers. In thisthesis, the lanthanide ions and Ag(I) ions were selected as templates, andpolycarboxylic acids were chosen as linkers/counterions to constructMOFs with novel and fascinating crystal structures, and the thermalproperties of some MOFs were investigated. 1. Five lanthanide-based MOFs,[Ln₃(bpdc)₄(Hbpdc)(H₂O)₂]·12H₂O(Ln=Ce(1), Nd(2) and Pr(3)) and [Ln₂(bpdc)₃(H₂O)₃]·3H₂O (Ln=Er(4)and Tm(5)) were obtained from2,2'-bipyridine-6,6'-dicarboxylate acidand corresponding lanthanide salts by the hydrothermal synthesis method.Single-crystal X-ray diffraction reveals that compounds1-3areisomorphous and isostructural, composed of one-dimensional (1D)infinite double zigzag chain structure, and further extended totwo-dimensional networks via hydrogen bonds and Ï€-Ï€ interactions;while isomorphous and isostructural compounds4-5are zero-dimensionaldiscrete moieties and further joined into three-dimensional (3D)framework by rich intermolecular hydrogen bonds and Ï€-Ï€ interactions.In (1)-(3), there are two distinct lanthanide ions with differentcoordination spheres in the structure, namely eight-coordinateddodecahedron and nine-coordinated tricapped trigonal prism geometries.The temperature of dehydration and decomposition of compounds1-5rises with the increase in the atomic number of lanthanide elements,which resulted from the lanthanide contraction in accordance with thedecrease of Ln-O and Ln-N bond distances.2. Two lanthanide based metal-organic frameworks,Ce₄Ag₂(bpdc)₄(SO₄)₃(H₂O)₆·H₂O (6) and La₂(bpdc)₃(H₂O)₄·2H₂O (7),were obtained from2,2'-bipyridine-4,4'-dicarboxylate acid andcorresponding lanthanide salts by the hydrothermal synthesis method.The single crystal X-ray diffraction reveals that compounds (6) and (7)are composed of3D frameworks built up of bpdc and lanthanide ions, inwhich the hydrogen-bonding interactions and Ï€-Ï€ stacking interactionsplay an important role in strengthening the frameworks. In compound (6),there are two distinct Ce³⁺atoms with different coordination spheres in thestructure, namely eight-coordinated dodecahedron and eight-coordinated bicapped trigonal prismatic geometries. While in compound (7), La³⁺atom is in an eleven-coordinated icosahedron environment. In bothcompounds (6) and (7),2,2',4,4'-bpdc acts as a multi-dentate ligand.3. Three lanthanide based metal-organic frameworks,[Ln₂(bdc)₃(phen)H₂O]·H₂O (Ln=La(1), Pr(2) and Yb(3)) were obtainedfrom1,3-benzenedicarboxylic acid (H₂bdc),1,10-phenanthroline (phen)and corresponding lanthanide(III) salts by the hydrothermal synthesismethod. Single-crystal X-ray diffraction reveals that compounds1-3areisomorphous and isostructural, composed of2D sheets constructed fromdbc and lanthanide ions and further extended to3D supramolecularframework through Ï€-Ï€ interactions between phen rings of theneighboring chains. In all of the three MOFs, there are two distinct Ln³⁺ions with different coordination spheres in the structure, namelyeight-coordinated dodecahedron and seven-coordinated pentagonalbipyramidal geometries. The bdc acts as both tetra-monodentate ligand tolink two Ln1and two Ln2ions (Ln=La(1), Pr(2) and Yb(3)), respectively,and counter-ions to balance the charge of the title complexes.Thermogravimetric analyses of1-3display a considerable thermalstability, and the temperature of dehydration and decomposition ofcompounds1-3raises with the increase in the atomic number oflanthanide elements, which resulted from the lanthanide contraction inaccordance with the decrease of Ln-O and Ln-N bond distances.4. A novel erbium based metal-organic framework,[Er₂(HO-bdc)₂(m-bdc)(phen)]·3H₂O (11), was obtained by thehydrothermal method from5-hydroxy-1,3-benzenedicarboxylic acid(HO-H₂bdc),5-methyl-1,3-benzenedicarboxylic acid (m-H₂bdc),1,10-phenanthroline (phen) and erbium(III) salt. Single-crystal X-raydiffraction reveals that the titled compound is composed of3Dframework of [Er₂(HO-bdc)₂(m-bdc)(phen)], in which three lattice water molecules are situated. The rich hydrogen bonding interactions togetherwith aromatic Ï€-Ï€ interactions of phen rings and coordinate-covalentinteractions between metal ions and organic ligands strengthen thestability of the3D erbium-based metal-organic framework. In compound(11), compound1possesses two crystallographically independent Er(III)atoms, namely eight-coordinated distorted square antiprism andnine-coordinated distorted tricapped trigonal prism.5. The reaction of AgNO₃,4,4'-bipyridine (bpy)/1,2-di(4-pyridyl)ethylene(dpe), hexanedioic acid (ha)/pyridine-3,5-dicarboxylic acid (pdc)/3,3'4,4'-biphenyltetracarboxylic acid (bptc) in alcohol aqueous solutionproduces block-like crystals of [Ag₂(bpy)₂](ha)₂·6H₂O(12),[Ag₂(bpy)₂(H₂O)](pdc)·3H₂O (13)[Ag₄(bpy)₄](bptc)·14H₂O (14) and[Ag₂(dpe)₂(H₂O)₂](ha)·6H₂O (15) at room temperature. All of theabove-stated compounds consist of parallel1-D infinite bpy/dpe-silvercationic chains, interspersed with organic anions which play the role ofcharge compensation in the crystal structure. The lattice water moleculesare situated among the framework of the crystal structure and stabilizedby rich hydrogen-bonding interactions, and lattice water molecules mayplay a role in the orientation of the organic anions in the crystal packing.All of the four complexes contain sandwich-like crystal structures, inwhich anionic sheets built up from different anions (ha^2-, pdc^2-, bptc^4-)and lattice water molecules via rich hydrogen-bonding interactions areinserted between the cationic silver complexes layers.In this paper, eleven lanthanide based metal-organic frameworks(MOFs) were obtained from the hydrothermal syntheses methods and theinfluence of flexible (like2,2',6,6'-bpdc and2,2',4,4'-bpdc) and rigid(like1,3-bdc, OH-bdc and m-bdc) polycarboxylic acids on the crystalstructures of MOFs was investigated. And four silver-based MOFs wereharvested via slow evaporation, and the different counterions (anions) play important roles in forming the crystal strucutures. The successfulsyntheses of these fifteen compounds enrich the family of MOFs, and willfacilitate the exploration of new MOFs with charming topologies andversatitle properties.