Assembly, Structures And Properties Of Coordination Polymers From Transition Metal With Pyridine-2,6-dicarboxylic Acid N-oxide

The design and construction of metal-organic coordination polymers is of current interest in the fields of supramolecular chemistry and crystal engineering. Major reasons for this interest stem from their intriguing variety of topologies and structural diversity, such as helixes and diamonded nets, and because of their potential applications as functional materials, such as heterogeneous catalysis, molecular recognition, magnetism, gas storage, ion exchange, nonlinear optics, and electrical conductivity. The prime importance in crystal engineering is how to obtain materials with prospective structures and function by choosing and designing suitable building blocks (tectons) and using some specific assembly strategy. This is also one of the most challenging research domains nowadays. In this paper, with the aim of preparing novel materials with beautiful architecture and excellent physical properties, we select pyridine-2,6-dicarboxylic acid N-oxide as building blocks to construct coordination polymers with selected transition metal ions guided by assembly principle of coordination polymer crystal engineering. We study on the coordination behavior (such as coordination abilities, coordination modes and the structures of complexes) of the ligand completely, and research the possible influence factors to the produces under different reaction condition. Six coordination polymers have been synthesized under hydrothermal conditions and others and structurally characterized by Single-crystal X-ray diffractometer. They are listed as follows: [Ag₂(pydco)]_n (1), [Zn(pydco)(H₂O)]_n(2), [Cu(pyco)₂]_n(3), {[Cu₂(pydco)₂(4,4'-bipy) (H₂O)]·2H₂O}_n(4), {[Cu₂(pydco)₂(bpe)(H₂O)]·2H₂O}_n(5), {[Cu₂(pydco)₂(bpa) (H₂O)]·2H₂O}_n(6). 1 is an 2D coordination polymer bearing 1D infinite silver strings constructed by Ag-Ag contacts; 2 is a 2D network structure containing double helical chains; While 3 is a 1D chain structure formed from in situ decarboxylation of pydco with strong aromatic n-n interactions between the pyridyl units of the intra-chain; 4-6 are infinite 1D chain structures which are composed of {Cu₂(pydco)₂} dimmer units and 4,4'-bpy, bpe, bpa linkages respectively. Important, the chains are expanded into three dimensional networks with 1D channel which contains tetra-water units by intermolecular hydrogen-bonding and aromaticÏ€-Ï€interactions. The elemental analysis, IR spectra, fluorescence spectra, and magnetic analysis for the compounds are discussed.