Modified polyoxometalate: a novel monocapped bi-supporting and reduced α-Keggin structure {PMo12O40[Cu(2,2′-bpy)]}[Cu(2,2′-bpy)(en)(H2O)]2

A novel modified polyoxometalate, {PMo12O40[Cu(2,2'-bpy)]}[Cu(2,2'-bpy)(en)(H2O)](2) [2,2'-bpy is 2,2'-bipyridyl (C10H8N2) and en is ethylenediamine (C2H8N2)], has been synthesized hydrothermally and structurally characterized by elemental analysis, TG, IR, XPS and single-crystal X-ray diffraction. The structural analysis reveals that the compound contains the reduced Keggin polyanion [PMo12O40](6-) as the parent unit, which is monocapped by [Cu(2,2'-bpy)](2+) fragments via four bridging O atoms on an {Mo4O4} pit and bi-supported by two [Cu(2,2'-bpy)(en)(H2O)](2+) coordination cations simultaneously. There exist strong intramolecular pi-pi stacking between the capping and supporting units, which play a stabilizing role during the crystallization of the compound. Adjacent POM clusters are further aggregated to form a three-dimensional supramolecular network through noncovalent forces, hydrogen bonding and pi-pi stacking interactions. In addition, the photocatalytic properties were investigated in detail, and the results indicated that the compound can be used as a photocatalyst towards the decomposition of the organic pollutant methylene blue (MB).