Unprecedented {Fe-14}/{Fe-10} Polyoxotungstate-Based Nanoclusters with Efficient Photocatalytic H-2 Evolution Activity: Synthesis, Structure, Magnetism, and Electrochemistry

摘要

Novel Fe-10 and Fe-14 clusters Rb9Cs4H37Fe10O34(A-alpha-PW9O31)(3)(OH)(3)center dot 36H(2)O (1) and H3Rb3Fe14(OH)(12)(PO4)(6)(B-alpha-PW9O34)(2)center dot 21H(2)O (2) were synthesized and characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA), and magnetic studies, and in solution by electrochemistry. Cluster 1 is a decameric Fe-III polyanionic cluster encapsulating a cesium atom in the center. Cluster 2 is a unique tetradecanuclear FeIII sandwich structure with phosphate-linked units featuring two quasicubic Fe4O4 moieties. Apparently, 2 has the highest nuclearity of all known Fe-III sandwich-type polyoxometalate clusters. Clusters 1 and 2 also act as photocatalysts with platinum as cocatalyst for H-2 evolution from light-driven water splitting. Changes in the cyclovoltammetric patterns with variations in pH were observed for 1 and 2, most likely due to intermolecular interactions among the high-nuclearity Fe-III cluster cores and subsequent changes in the acid-base properties of the two reduced POMs. Magnetic studies provide evidence of antiferromagnetic interactions in 1 and 2. TGA showed that complexes 1 and 2 decompose between 580 and 590 degrees C.