The Synthesis Of Macrocycles Containing Nitrogen And Oxygen Donor Atoms And The Study Of Host-guest Recognition

In this paper,macrocycles L₁,L₂ and L₃ were synthesized and their structures were characterized by ¹H NMR and MS,and the crystal structures of macrocyclesL₁andL₂ were obtained.The[1+1]Schiff base macrocyclic compound L₁ containing both isophthalamide unit and phenol ringshas been synthesized from the reaction of precursors N,N'-?6-amino-2-pyridyl?-1,3-dicarboximide with 5,5'-methylenebis-salicylaldehyde by Schiff-base condensation reaction.The macrocycle L₁ was characterized via¹H NMR,FABMS and elemental analysis.The crystal structure of L₁was determined by X-ray diffraction analysis and it has a folded clamp conformation.In the solid state of L₁,individual macrocycles were assembled into columnar structures with 1D channel through intermolecular hydrogen bonding and?–?stacking interactions.The results show that macrocycle L₁displays a selective recognition ability for H₂PO₄^-and HP₂O₇^3-anion respectively by the coordination reaction of L₁with a series of anions using UV-Vis absorption spectra technique.Furthermore,the coordination reaction of L₁with H₂PO₄^-or HP₂O₇^3-anion was investigated via UV-Vis spectra,¹H NMR and the isothermal titration calorimeter?ITC?respectively.The stoichiometric ratio,the association constant?K?and the thermodynamic parameters??_rH_m,?_rS_m and?_rG_m?of the coordination reaction were obtained as well.The results show that the macrocycle L₁binds H₂PO₄^-with a 1:1binding stoichiometry and binds HP₂O₇^3-to form a structure of sandwich-typewith a bonding ratio of 2:1.The Schiff base macrocyclic compound L₂ containing both 2,6-diamidopyridine and pyrrole unitshas been synthesized and the single crystal structure was obtained by improving the synthetic method inreported literatures.Moreover,the experimental result shows that the product could transform from the[1+1]macrocycle L₂ to[2+2]macrocycleL₃ by adding water to methanol solvent.The pure[2+2]macrocycle L₃ was obtained by column chromatography and thestructure was characterized by¹H NMR and MS.Furthermore,we investigated the influence of three factors,i.e.the concentration of the precursor and temperature,on the non-covalent self-assembly processbased on[1+1]macrocycleL_2.In addition,the coordination reaction of L₂ with Cu²⁺,Zn²⁺and Ni²⁺ions was investigated via UV-Vis spectratechnique,and the coordination ratio and equilibrium constant were obtained.The results show that the coordination ratio of macrocycleL₂withall three ions is 1:1,and the equilibrium constants of macrocycleL₂with Cu²⁺,Zn²⁺and Ni²⁺ions are K_a=7.6013×10⁶M^-1,K_a=6.1008×10⁶M^-1 and K_a=1.8447×10⁶M^-1,respectively.