Synthesis,Characterization And Properties Of Catechol Functionalized Azoxanthraquinone Macroring

Anthraquinone and catechol are natural substances widely present in nature.They not only have important biological functions,but also have good application prospects in molecular recognition.In order to improve the recognition ability of guest molecules,a lariat anthraquinone macrocycle functionalized with catechol（H₂L）was synthesized via Mannich reaction.Its structure were confirmed by NMR,MS,IR,TG,elemental analysis and crystal structure.The Mannich base（H₂L）can be partially decomposed into L1·3H₂O and HL1·NO₃·2H₂O in the presence of TBAOH/Al（NO₃）₃·9H₂O in DMSO.Free L1·3H₂O is essentially coplanar while protonated HL1·NO₃·2H₂O is highly distorted by crystal structure.The introduction of catechol will make the cavity of the macrocyclic larger.Chloride of Li⁺,Na⁺,K⁺,Cs⁺,Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺,Fe³⁺,Cu²⁺,Zn²⁺,Al³⁺shift Ep of anthraquinone to positive by DPV,especially the second reduction peak of anthraquinone（-0.75 V）.Fe³⁺,Zn²⁺,and Al³⁺change the reduction of catechol fundamentally（-0.33 V）.0.50 m M H₂L shows chromogenic response to FeCl₃ and Fe（NO₃）₃ to form uncommon 2:1 and 3:2（H₂L:Fe）complexes,both peaking at 748 nm in DMSO.In the presence of 2 eq Na OH,the 748 nm absorbance shifts to 777 nm,identical to Fe₂（HL）₂Cl₄ in DMSO.Solvent,concentration,reaction time and the addition of alkali has a significant impact on the structure of the complex.Dark green FeCl₃·H₂L·2H₂O powder and Fe₂（HL）₂Cl₄ crystal can be isolated from ethanol in high/low H₂L concentration,through the research methods such as elemental analysis,IR,thermogravimetric found solid powder FeCl₃·H₂L·2H₂O is not remove protons complexes while Fe₂（HL）₂Cl₄ remove protons fully.The phenomenon that catechol coordinated with iron（III）without deprotonation has not been reported in the literature.H₂L reacts quickly with FeCl₃,while the reaction with Fe NO₃ is quite slow.The crystal structure determination shows that Fe₂（HL）₂Cl₄ is a binuclear complex,the Fe（III）in Fe₂（HL）₂Cl₄adopts a less common pentacoordination with three catecholate oxygen and two chloride in dimer.The anthraquinone and catechol surround the Fe₂O₄Cl₄ to form a wheel structure.The same as L1·3H₂O,HL1·NO₃·2H₂O and H₂L,the distortion of inbound C=O is much high than outbound C=O in anthraquinone in all these compounds.0.50 m M H₂L also shows chromogenic response to fluorides and hydroxides,which peak at 670 and 684 nm respectively in DMSO.The binding ratio between H₂L and F^-/OH^-is 1:2.In higher concentration of hydroxides,684 nm greenish blue 1:2complex gradually transforms to red complex and peaks at～530 nm in minutes at room temperature.No color change can be observed in ethanol solution in the presence of OH^-.