Synthesis And Structure Of Supramolecular Complexes Based On Multi-carboxylic Acids

In recent years, supramolecular complexes constructed by carboxylic acids through both covalent bond and weak interactions have attracted great interest of chemists. This is not only because of their intriguing structural frameworks but also account for their potential applications in catalysis, electronic and magnetic materials, microporous materials and nonlinear optics materials. In this thesis, a series of complexes based on aromatic multicarboxylic acids have been successfully synthesized in solutions or under hydrothermal conditions. Their structure and properties are investigated.1. Four discrete structural complexes were synthesized in the solution with the ligand p-phenylenediamine--N,N,N',N'-tetraacetic acid(p-PhDTA) and 2,2'-bipyridine, pyridine and oxalate: [Ni₂L(2,2'-bipy)₂ (H2O)₂] ·4H₂O(1) , [Co₂L (2,2'-bipy)₂ (H₂O)₂] ·4H₂O(2) , [Co₂L(pyridine)₂(H₂O)₄]·4H₂O(3), [Gd₂(C₂O₄)(H₂L))₂(H₂O)₁₀]·6H_<sub>2O(4). The IR spectra and X-ray diffractions reveal that complexes 1-3 are dinuclear which was bridged by the p-PhDTA ligand in their crystals. The ligand p-PhDTA is hexdentate and the central ions are all six coordinated in a distorted octahedral geometry. There are a lot of crystal waters and coordinate waters in the complex . Abundant hydrogen bonds are observed between these waters and uncoordinate O from carboxylic group. Hydrogen bonds extend the discrete structure into 2D or 3D supramolecular structure. There are Ï€-Ï€ stacking in the complex between the aromatic rings and heteroatomic rings. The stacking effect makes the supramolecular structure more stable. Complex 4 contains two monodentate p-PhDTA in its structure. The two rare earth ions are bridged by the oxalate ligand and there are five coordinate waters in each unit. Six crystal waters are around the main structure. The coordinate waters and uncoordinated waters are served both as donor and accepter to give a 3D hydrogen network in the crystal of complex 4.2. Three one dimensional chain coordinate polymer based on 2,5-pyridinedicarboxylic acid are synthesized in solution: {[Co(H₂O)₄][Co(C₇H₃O₄N)₂(H₂O)₂]·4H₂O}∞(5), {[Mn(H₂O)₄] [Mn(C₇H₃O₄N)₂(H₂O)₂]·4H₂O}∞(6), {[Cu (C₇H₃NO₄)(H₂O)]·2H₂O}∞ (7). The X-ray diffractions show that compound 5 and 6 are isomorphous. The carboxylic group in the ortho-position of N in the 2,5-pyridinedicarboxylic acid servers as a bridge to link the transition metals into one dimensional chain. Another carboxylic group remains uncoordinated. In the complex 7, the ligand 2,5-pyridinedicarboxylic acid acts as a bridge to connect the Cu²⁺ ions through the two carboxylic group. Each Cu²⁺ is four coordinate and Cu···O weak interaction was...