Syntheses, Structures, And Properties Of Pyridine-Containing Asymmetric Tripodal Ligands And Their Complexes

The design and construction of metal-organic architectures has been received considerable attention not only because of their intrinsic aesthetic appeal in structures but also because of their potential application in catalysis, molecular adsorption, magnetism and non-linear optics. A lot of research showed that the conformation, size and coordination number of ligands, the metal geometry and the counteranions influence greatly on construction of the coordination complexes. It is important to rationally design ligands and to choose metal salt. Syntheses, structures, and properties of pyridine-containing asymmetric tripodal ligands and their complexes are studied in the paper. Tripodal ligands are reported extensively to construct metal-organic complexes with fascinating structures through self-assembly process. In this thesis, we developed a few of tripodal ligands and explore their complexes under hydrothermal condition.1. Syntheses and characterization of a series of 3,5-bis(pyridylmethoxy) benzoic acids3,5-Bis(pyridylmethoxy) benzoic acids (2-ms,3-ms,4-ms) (Fig.1)were prepared from 3,5-dihydroxy benzoic acid and chloromethyl pyridine. Three target compounds and intermediate products were characterized by IR,1H NMR and 13C NMR spectra.2. Syntheses and characterization of a series of pyridylmethyl 3,5-bis(pyridinyl methoxy)benzoates Nine compounds of (2z2m, 2z3m, 2z4m, 3z2m, 3z3m, 3z4m, 4z2m, 4z3m, 4z4m) (Fig.2) were prepared from 3,5-dihydroxy benzoic acid and chloromethyl- pyridin via esterification, etherification. The nine target compounds and intermediate products were characterized by IR,1H NMR and 13C NMR spectra. The separation condition of raw 4z4m by HPLC was discussed.3. Syntheses and structures of complexes based on ligand 3,5-bis(pyridylmethoxy) benzoic acids (2-ms, 3-ms, 4-ms)Complex (I) is a simple compound. It crystallized in monoclinic space group P2(1)/c. Ni2+ ion has an octahedral geometry consisting of six water molecules. 2-ms only acts as counteranion. Components in the molecules are connected by hydrogen bonding andπ-πinteraction into a 2D structure.Complex (II) is a two dimensional ladder structure. It crystallized in monoclinic space group Cc. Co2+ adopts six-coordinated distorted octahedal geometry consisting of four carboxylic O atoms from two ligands and two pyridyl N atoms from another two ligands. In 3-ms, the carboxylic group chelates to Co2+ and only one pyridyl N atom participates in coordination (this coordination mode is abbreviated as L-2).The crystal of complex (III) is triclinic with space group P-1. Cd2+ adopts seven-coordinated distorted pentagonal bipyramidal geometry consisting of four carboxylic O atoms from two ligands, three pyridyl N atoms from another three ligands. There are two coordination modes for ligands in (III), one of which is an aforementioned L-2 coordination mode, but the other is that carboxylic group and two pyridyl groups all participate in coordination (this coordination mode is abbreviated as L-3). This complex is a two-dimensional bilayer structure, in which each layer consists of hexagonal lattices built up by ligands with L-3 coordination mode linking Cd2+, while two layers are linked by ligands with L-2 coordination mode.The structures of complex (IV) and (V) are analogous with a one-dimensional zigzag infinite chain. They crystallized in monoclinic with space group C2/c. Carboxylic group in ligand adopts monodentate coordination mode to coordinate to metal ion. The central metal ion (Ni2+,Co2+) has a six-coordinated distorted octahedral geometry consisting of two water molecules, two pyridyl N atoms from two ligands, and two carboxylic O atoms from another two ligands.4. Syntheses and structures of two complexes [Hg3Cl6(4z4m)2·2H2O]n (VI) and [Hg2I4(4z4m)2]n (VII) based on ligand 4z4mThese two complexes are synthesized under solvothermal condition. The crystal of complex (VI) is monoclinic with space group P2/c. Hg2+ has four-coordinated distorted tetrahedral geometry consisting of two Cl- anions and two pyridyl N atoms from two ligands. Ligand adopts tridentate coordination mode linking three Hg2+. A chair-like octagon is formed by interlinking of four ligands and four Hg2+ ions. Two neighboring octagons share two laterals to form a one-dimensional infinite chain.The crystal of complex(VII) is orthorhombic with space group Pbcm. Hg2+ also adopts four-coordinated distored tetrahedral geometry consisting of two I- and two pyridyl N atoms from two ligands. Ligand adopts a tridentate coordination mode linking to three Hg2+ ions. Two ligands and two Hg2+ ions are interlinked into one V-shaped quadrilateral and two neighboring quadrilaterals are linked by one Hg2+ ion into one-dimensional helical chain.Solid fluorescent properties of ligand 4z4m, complexed were detected. In comparison with 4z4m, the observed emissions of complexes (VI) and (VII) are contributed to intraligandπ-π* transition.