Assembly,Structure,and Catalytic Properties Of Metal-organic Cycles/Cages Based On Bisimidazole-schiff Base Ligands

Metal-organic cycles and metal-organic cages,as classical supramolecular complexes,are formed by metal ions with specific coordination configurations as receptors and organic ligands as donors.This is well suited to materials designed to simulate the structure and function of biological systems.In this paper,two diimidazole schiff base ligands H₂L1/H₂L2 were designed and chelated with Cu^II to form the metal ligand Cu（HL1）/Cu（HL2）.Two metal organic cycles 1[Cu₃^I(Cu^IIL1)₃]（Cl O₄）₃,2[Cu₃^I(Cu^IIL2)₃]（Cl O₄）₃,and two heterometallic metal-organic cycles 3[Ag₃^I(Cu^IIL1)₃]（NO₃）₃,4[Ag₃^I(Cu^IIL2)₃]（NO₃）₃.It was found that the Cu^II/Cu^I metal-organic cycles can catalyze oxidation of alcohols to aldehydes mediated by co-catalyst TEMPO（2,2,6,6-tetramethylpiperdine-1-oxyl）with ambient air as oxidant,Cu^II/Ag^Imetal-organic cycles has no catalytic effect.Next,a triangular prism 5{[Cu₃^I(Cu^IIL1)₃]₂L2₃}（Cl O₄）₈（H₃O）₂ was assembled in a 2:3 ratio with metal-organic cycle 2 as the panel and triethylenediamine as the bidentate columnar ligand.Experiment has found that the triangular prism 5 interacts with oxygen in the air in the solvent,Cu^I is oxidized to Cu^II,and the structure is transformed from the triangular prism 5 into a bicapped square antiprism cage 6[Cu₁₀L₈]（Cl O₄）₄.The organic molecule N-methylimidazole can accelerate the conversion process,and triangular prism 5 also has the same catalytic ability as the mixed-valence metal-organic cycles,which can quickly and effectively catalyze the oxidation of alcohols to aldehydes.This work provides a new method for the design and assembly of triangular metal-organic cycles and triangular cage,a new idea for the synthesis of green aerobic alcohol oxidation catalysts,and a new example for the understanding of cage-to-cage transformation induced by stimulation.