Double Sandwich Polyoxometalate and Its Fe(III) Substituted Derivative, [As2Fe5Mo21O82]17– and [As2Fe6Mo20O80(H2O)2]16–

A double sandwich polyoxometalate and its Fe­(III) substituted derivative, [As2Fe5Mo21O82]17– (1) and [As2Fe6Mo20O80(H2O)2]16– (2), were synthesized and characterized by single-crystal X-ray diffraction, infrared spectroscopy, fluorescent spectroscopy, UV spectra, thermogravimetry-differential scanning calorimetry analyses, electrospray ionization mass spectrometry, and magnetism measurements. The polyoxoanion is composed of a central fragment FeMo7O28 for 1 (Fe2Mo6O26(H2O)2 for 2) and two external AsMo7O27 fragments linked together by two distinct edge-sharing dimeric clusters Fe2O10 to lead to a C2v molecular symmetry. The central FeMo7O28 fragment and external AsMo7O27 fragment have a similar structure, and both of them can be viewed as a monocapped hexavacant α-Keggin subunit with a central FeO4 group or a central AsO3 group. Both of the polyoxoanions contain a oxo-bridged FeIII5 magnetic core with the angles of Fe–O–Fe in the range of 96.4(4)–125.7(5)°, and magnetism measurements show an overall ferromagnetic interactions among the five-nuclearity cluster Fe5 with the spin ground state S = 15/2.本研究合成了双夹心型多金属氧酸盐（double sandwich polyoxometalate）及其铁(III)取代衍生物，即[As₂Fe₅Mo₂₁O₈₂]¹⁷⁻（编号1）与[As₂Fe₆Mo₂₀O₈₀(H₂O)₂]¹⁶⁻（编号2），并通过单晶X射线衍射、红外光谱、荧光光谱、紫外光谱、热重-差示扫描量热分析、电喷雾电离质谱及磁学性能测试对其完成了表征。该多阴离子的结构组成为：化合物1的中心结构单元为FeMo₇O₂₈，化合物2的中心结构单元为Fe₂Mo₆O₂₆(H₂O)₂；两个外部的AsMo₇O₂₇结构单元通过两个独立的共边双核Fe₂O₁₀簇相互连接，最终形成具有C₂v分子对称性的整体结构。中心FeMo₇O₂₈结构单元与外部AsMo₇O₂₇结构单元具有相似的拓扑结构，二者均可被视作以中心FeO₄基团或AsO₃基团为核心的单帽六缺位α-Keggin结构单元。两种多阴离子均含有氧桥连的FeIII₅磁核，其Fe–O–Fe键角范围为96.4(4)°~125.7(5)°；磁学性能测试结果显示，该五核Fe₅簇内存在整体铁磁相互作用，其基态自旋为S=15/2。