Coordination-driven Self-assembly And Properties Of The Metal-Organic Macrocycles

Metal-organic polygons are a group of 2D supramolecular complexes which are built from metal ions and organic ligands based on coordination-diven self-assembly.They have wide application potential in molecular recognition,ion detection,drug-delivary and catalysis.Compared to step-wise covalent synthesis,coordination-diven self-assembly has great advantages in mild reaction condition and high yields synthesis,predictabe and controllable structural design etc,which has promoted the development of supramolecular chemistry and enriched the modern synthetic techneques.This thesis focuses on the coordination-diven supramolecular self-assembly of mental-organic macrocycles and studies on the induced-fit transformation mechnism,anion reccepter chemistry,gel and fluorescence properties.The main conclusions are as follows:1.Design and synthesis of a semirigid bis（benzimidazole）ligand bridged by methylene,which is not conjugated and bears two acidic CH groups as hydrogen-bond donors.A family of metal-organic macrocycles with empirical formula of Pd_nL_2n（n = 3,4,5,6,7）are selectively obtained starting from this simple ligand and palladium ions.Five distinct macrocycles are clearly characterized by NMR,ESI-TOF-MS,and in the case of n = 3,4,5,6 by single-crystal X-ray diffractions.Hydrogen-bonding interactions between the inner surface of the macrocycles and the anionic templates dictated the shape and size of the products.2.Based on titration experiments,we manage to draw a comprehensive map detailing the induced-fit transformation processes betweem all species of the Pd_nL_2n.The(HMo₇O₂₄)@Pd₅L₁₀ was found to be the most stable host-guest complex for this dynamic combinatorial system,which could be quantitatively obtained by additon of（t-Bu₄N）₆Mo₇O₂₄ to either compounds Pd₃L₆,Pd₄L₈,Pd₆L₁₂ or Pd₇L₁₄.In fact,this host-guest complex is so stable that once formed it will never transform into other macrocycles.Similarly,Pd₃L₆ could be quantitatively obtained by the templation effect of the NO₃^-anion starting from Pd₄Lg,Pd₆L₁₂ or Pd₇L₁₄.In particular,Pd₇L₁₄ can be converted into any other mental-organic macrocycles based on different anions.Based on a careful assignment of the NMR and ESI-TOF-MS datas,it is found that transformation of Pd₇L₁₄ into Pd₃L₆ takes place through Pd₆L₁₂,Pd₅L₁₀ and Pd₄L₈ intermediates.We hypothesize that hydrogen-bonding between host and anions are acting as anchors which pull and dissociate the framework,leading to a gradually shrinking of the ring size.Hydrogon-bonding between host and anions also play an important role in the sol-gel transformation process,where a gel material can be obtained by the induction of NO₃^-.3.A Pd₂L₄ container-type macrocycle is synthesized from a tetraphenylethylene（TPE）based bidentate ligand.On the one hand,we studied the aggregation-induced emission（AIE）effect about this supramolecular compound by adding ethyl acetate.On the other hand,hydrogon-bonding between host and anions can restrict the rotation of the phenyl rings attached to the C=C bond,from which we explored the anion-responsive fluorescence properties of the host.We conclude that this molecular nanocontainer can serve as potential fluorescent sensor toward anions.