Syntheses,Structures And Propertities Of Coordination Compounds With Pyridinium-Carboxylate/Phosphonate Zwitterionic Ligands

Coordination polymers are coordination compounds whith extended one-, two-or three-dimensional structures built from metal ions and organic bridging ligands through coordination bond and sometimes other assistant weak interactions such as H-bonds or π-π stacking interactions. Di-and multicarboxylate ligands with neutral backbones are among the most widely used organic building blocks for the construction of coordination polymers, while the zwitterionic carboxylate ligands bearing positive backbones (such as pyridinium) have been much less commonly utilized in coordination chemistry.It has been shown that zwitterionic pyridinium-carboxylate ligands, in which the negative charge of the carboxylate groups is at least partially compensated by positive pyridinium, is in favor of the simultaneous coordination of other anions and thus can lead to coordination structures that are difficult to access with ordinary carboxylate ligands. Furthermore, the electron-defficient character of the pyridinium group may import new functions to coordination polymers.With these in mind, this thesis designed and synthesized new pyridinium-containing zwitterionic ligands with new features (rigid dicarboxylate ligands and bifunctional ligands bearing both carboxylate and phosphonate coordinative groups). The ligands were used to synthesize coordination compounds with various metal ions, and the compounds were characterized by means of single-crystal and powder X-ray diffraction, IR and UV-Vis spectra, and thermogravimetric analysis. Magnetic and photochromic studies were performed with relevant compounds. The main results are summarized as follows:1. Studies with 1-(4-carboxylphenyI)pyridinium-4-carboxylate inner salt (L1)The L1 ligand consists of directly bonded phenyl-4-carboxylate and pyridinium-4-carboxylate moieties. In the fully-deprotonated form, the dicarboxylate ligand is monoanionic due to the presence of pyridinium, but geometrically, it features the linearity, length and rigidity similar to the well-known dianionic 4,4’-biphenyl dicarboxylate ligands but distinct from previously studied zwitterionic dicarboxylate ligands. With this ligand we got three isomorphous one-dimensional complexs [M(L1)H2O)2]·2H2O (M= Mg(Ⅱ), Mn(Ⅱ), Co(Ⅱ)). In their structures, the metal ion is coordinated in a trans-octahedral geometry with four monodentate carboxylates from different L1 ligands and two water molecules. The metals are linked into 1D chains via the L1 ligands, and the chains are associated via a plenty of O-H...O and π-π interactions to give a 3D supramolecular architecture.Under different conditions, three isostructural 3D coordination polymers of formula [M(L1)2]·nH2O(M= Co(Ⅱ),Zn(Ⅱ)or Cd(Ⅱ)) have been synthesized. In the structures, tetrahedrally coordinated metal ions are linked into diamond-like 3D networks by L1, in which each carboxylate group is monodentate. The diamond networks are 6-fold interpenetrated, which still leaves void space accessible to water guest molecules. Further studies with the relatively stable Zn(Ⅱ)compound indicated photochromic properties. This is the first photochromic compounds built from a non-photochromic monopyridinium ligand. The photochromic properties were studied with UV-vis, fluorescence, electronic paramagnetic resonance, and X-ray photoelectron spectroscopy. The mechanism was proposed to be photo-induced electron transfer, which produces a pyridinium radical. It was also found that the photochromic process is accompanied by fluorescence quenching.2. Studies with 1-(4-carboxylphenyl)pyridinium-3-carboxylate inner salt (L2)Ligand L2 is similar to L1 except that the coordination orientation is changed due to the 3-carboxylate group in the place of 4-carboxylate. With this rigid but non-linear ligand, we got two isomorphous complexs of formula M(L2)2(H2O)4 (M= Mn(Ⅱ), Co(Ⅱ)). In their structures, metal ions coordinate with two ligands and four H2O to produce trans-octahedral units. The units are extended to 2D layers with uncoordinated ligand via a plenty of O-H...O, even 3D supramolecular architecture connected by ligands.3.Studies with 1-(2-phosphonicylethyl)pyridinium-4-carboxylate inner salt (L3)The ligand simultaneously contains phosphonate and carboxylate moieties between which is N-ethylidence that can enhance flexibility of the ligand. We got Mn(II) compound of formula [Mn(L3)(H2O)]. In the structure, Mn(II) ions in sqaure pyramidal geometry are linked by PO3C tetrahedrons to generate a 63 coordination layer, and the layers are crosslinked by the N-ethylenepyridinium groups to give a 3D framework with the 65.8 topology. Magnetic data show that O-P-O bridge between metal ions transfers antiferromagnetic coupling.