Nitrous Macrocyclic Ligand And Its Functional Derivatives In Coordination Chemistry; New Bipyridine Ligand Supramolecular Architecture

This thesis consists of two parts: (I) Studies on the coordination chemistry of diaza-mesocyclic ligands and their functionalized derivatives (chapters 1?5); (II) Construction of supramolecular aggregates based on novel dipyridyl building blocks (chapter 6). Part I In chapter 1, the history and progress of the coordination chemistry of the most typical diazamesocycle, 1,5-diazacyclooctane (DACO), and its functionalized derivatives are concisely introduced and reviewed, and the research significance and main conclu-sions of this thesis are summarized. Chapter 2 covers our investigation of the structure, configuration and coordination chemistry of DACO in order to further elucidate some important features of this system. The crystal structure of [H2DACO]Br·ClO4 confirms that the "free"DACO ring is folded up into a stable boat-chair configuration in the solid state, which is consistent with that in its metal complexes. The crystal structures of [Ni(DACO)2]Br2 and [Ni(DACO)2]Br·ClO4·2H2O indicate that the [Ni(DACO)2]2+ cations in both complexes have different arrangements of DACO due to their crystallographic symmetries. Quantum chemical calculation has been carried out to investigate the stability of the two complexes and the results show that both coordination modes of [Ni(DACO)2]2+ are possible. Based on the analysis of the crystal structure of [Cu(DACO)2(SCN)]·(SCN)·2H2O, we clarified the effect of the disorder of the carbon atom in the methylene group on the configuration of the DACO ring, which plays an important role in dictating the coordination geometry of the metal center. A novel oxalato-bridged dinuclear CuII complex with DACO terminal ligands has been synthesized and its usual magnetic behavior observed. We concluded that the height of the metal centers above the basal coordination plane is also a significant factor that influences the magnetic coupling between CuII ions, which leads to development of a further magneto-structural correction for such systems. In chapter 3, the preparation and characterization of a series of mono-or bi-heterocyclic (quinoline, imidazole and pyridine) functionalized DACO derivatives and their CuII, CoII, NiII complexes are described. The crystal structures of these complexes show that doubly sub-stituted tetradentate heterocyclic ligands normally tend to form stable penta-coordinated [MLCl]+ type mononuclear complexes due to the boat-chair configuration of DACO, and the coordination geometries of the metal centers are changed according to their different steric bulk, which could serve as the model complexes of some metal-containing enzymes. On the other hand, mono-substituted tridentate heterocyclic ligands tend to form chloro-bridged binuclear or one-dimensional (1-D) alternate chain complexes, and the metal ions are also in a penta-coordinated environment. That is, the number of the pendant arm plays an important role in formation of these metal complexes. In addition, two 3-or 4-pyridyl substituted DACO ligands have been synthesized, and they form a 1-D coordination poly-mer or a bimetallacyclophane supramolecule as bridging ligands with CuII, respectively. The unexpected magnetic behavior of the latter, in which two CuII centers are bridged through weak coordination with chlorides, has been observed and clarified. This indicates that the super-exchange pathway of such dimers depends on various orbitals, which further develops the magneto-structural role proposed by Hatfield. In chapter 4, two DACO ligands bearing one or two phenol functional group(s) and their complexes are described. For a DACO ligand with two phenol pendants, phenoxo-bridged trinuclear complexes were obtained, whereas the mono-substituted ligand can form phenoxo-bridged binuclear complexes. In all these complexes, the DACO ring adopts the boat-chair configuration, resulting in the specific penta-coordinated geometries of the metal centers. The magnetic properties of these oligonuclear complexes have been inves-tigated and the magneto-structural corrections discussed in detail. Of further importance, using this strategy, we could prepare other phenoxo-bridged metal complexes and fur-ther understand the magnetic interactions in such systems. Based on all these findings, we can conclude that the nature of the pendant arm is a determining factor governing the structures and properties of its metal complexes. In chapter 5, we present the design and synthesis of three carboxylic-functionalized diazamesocycles, which could form a series of polynuclear supramolecular complexes with unique structures and properties. In these complexes, the versatile carboxylate groups ex-hibit a variety of coordination modes, which results in the fascinating chemistry and also makes it difficult to preorganize the coordination rules in these complexes. Three mononu-clear complexes in which the carboxylate groups coordinate to the metal centers with monodendate chelated mode have been directly prepared through the replacement ap-proach, which could be used as complex ligands to construct other homo-or hetero-metal-lic polynuclear complexes. Using different alkali templates, a unique 1-D coordination polymer with octahedral cage unit or dodecanuclear molecular aggregate with tetrahe-dral coordination cages bridged by a μ3-Cl have been separated. This result clearly indi-cates that the subtle change of the ligand and template is critical in the process of self-assembly. In addition, proton-controlled reversible inter-conversion between an achiral CuII molecular square and a 1-D spontaneously resolved chiral interpenetrated double-chain motif has been successfully achieved, which opens a new route in designing new functional materials with switching ability. The first tetranuclear NiII and CoII clusters with trigonal planar geometry, in which the DACO rings take the unusual boat-boat configura-tion and the metal centers show octahedral coordination, have been prepared. The mag-netic behaviors of these anisotropic systems were discussed in detail and the mag-neto-structural corrections developed. Part II In chapter 6, a concise introduction of the background of our work is presented firstly. The recent development on the roles of anions, which play different roles due to their different coordination ability, size of volume and template function, in construction of fascinating supramolecular structural topologies of organic-inorganic coordination polymers, is briefly reviewed. In the present research project, the angular dipyridyl bridg-ing ligand, 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo) and its 3,3'-N-donor analog 3-bpo have been chosen with regard to structural control of discrete or divergent supramolecular architectures, such as bimetallacyclophane, 1-D coordination chain, 3-D interpenetrating diamondoid topology and chiral 3-D metal-organic open framework, upon metal complexation with CuII under appropriate conditions. The present study clearly indicates that the nature of the counter anions play a key role in crystal engineering and suggests that, given the simple permutations of the anions, CuII alone might also have a rich and diverse role in construction of coordination frameworks. The thermal stability, removal-reintroduction of guest molecules, anion-exchange properties and magnetic behaviors of these interesting supramolecular species have also been investigated in detail.