亚铁金属有机层的合成、结构及其超快仿生催化性能

An Iron(Ⅱ) Metal-Organic Layer: Synthesis, Structure and Ultrafast Biomimetic Catalytic Performance

六水合四氟硼酸亚铁、三水合四氰基铂酸钾和4-甲基吡啶-N-氧化物在水和乙醇中自组装形成了一种新的二维金属有机框架(Fe-MOF)。单晶结构分析表明,Fe-MOF结晶于单斜空间群P2_(1)/c。在Fe-MOF中,每个[Pt(CN)_(4)]^(2-)通过氰基桥联4个Fe原子,而每个Fe原子与4个[Pt(CN)_(4)]^(2-)的N相连形成二维(4,4)网格结构。二维层之间通过范德华力沿c轴形成AB堆积,层间距约为0.6 nm。亚铁中心存在2种[FeN_(4)O_(2)]八面体配位环境,一种亚铁离子的轴向与2个水分子配位,而另一种亚铁离子的轴向与1个水分子和1个4-甲基吡啶-N-氧化物配位。Fe-MOF可通过超声剥离形成亚铁金属有机层(Fe-MOL)。红外光谱(FT-IR)和X射线粉末衍射(PXRD)分析表明,Fe-MOL保持二维晶态结构。扫描电子显微镜(SEM)和透射电子显微镜(TEM)表征显示Fe-MOL为纳米层状结构。原子力显微镜(AFM)分析结果表明Fe-MOL为5 nm左右超薄层状结构。得益于亚铁中心的配位环境与天然血红素相似,Fe-MOL在2,2′-联氮-双(3-乙基苯并噻唑啉-6-磺酸)二铵盐(ABTS)的催化氧化反应中展现出超快的催化速率和超高的催化效率,反应溶液在16 s内由无色变为深绿色,表观二级速率常数(k_(cat)/K_(m);k_(cat)为催化常数,K_(m)为米氏常数)高达4.70×10^(6)mmol^(-1)·L·s^(-1)。Fe-MOL具有良好的催化循环稳定性,5次循环后仍然具有90%的催化活性。Fe-MOL优异的催化效率超过了大部分已报道的MOF类仿生催化剂。

A new two-dimensional metal-organic framework(Fe-MOF)was self-assembled by ferrous tetrafluoroborate hexahydrate,potassium tetracyanoplatinate trihydrate,and 4-picoline-N-oxide in water and ethanol.Singlecrystal X-ray crystallography reveals that Fe-MOF crystallized in the monoclinic space group P2_(1)/c.[Pt(CN)_(4)]^(2-)is bridged by four Fe atoms through the cyano group,while Fe atom is connected with four N atoms from[Pt(CN)_(4)]^(2-),forming Fe-MOF with(4,4)-grid structure.Fe-MOF is stacked by a two-dimensional layer in an AB mode along the caxis by virtue of van der Waals forces,and the layer distance is 0.6 nm.The Fe􀃭centers have two[FeN_(4)O_(2)]octahedral coordination environments:one of them is connected axially with two water molecules,while the other is connected axially with a water molecule and a 4-picoline-N-oxide.Metal-organic layer(Fe-MOL)was prepared by ultrasonically exfoliating Fe-MOF.Fe-MOL maintained the two-dimensional crystalline structure as evidenced by infrared spectroscopy(FT-IR)and X-ray powder diffraction(PXRD).Scanning electron microscope(SEM)and transmission electron microscope(TEM)characterizations showed that Fe-MOL had a nanolayered structure.Fe-MOL was proved to be an ultra-thin layered structure of about 5 nm by atomic force microscopy(AFM).Fe-MOL exhibited ultrafast catalytic speed and ultrahigh catalytic efficiency in the catalytic oxidation reaction of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt(ABTS)due to the coordination environment of the Fe􀃭center possessing a similar natural heme structure.The color of the solution changed from colorless to dark green in just 16 s,and the apparent second-order rate constant(k_(cat)/K_(m);k_(cat) is catalytic constant,K_(m) is Michaelis constant)was as high as 4.70×10^(6)mmol^(-1)·L·s^(-1).Fe-MOL exhibited good cycle stability and it still had 90%catalytic activity after five catalytic cycles.The excellent catalytic efficiency of Fe-MOL exceeded most of the reported MOF biomimetic catalysts.CCDC:2121346,Fe-MOF.