A new polyoxometalate (POM) based on a flexible bidentate ligand and "inverted Keggin" inorganic building block, namely, [Cu8L8[Mo12O46(AsPh)(4)](2)]center dot H2O (1), where L is 1,3-bis(1,2,4-triazol-1-yl)propane, has been synthesized under hydrothermal condition. In 1, the "inverted Keggin" [Mo12O46(AsPh)(4)](4-) building blocks are linked by the one-dimensional (1D) zigzag [Cu-I(trans-L)](+) chains and [Cu-4(I)(cis-L)(4)](4+) macrocycles to yield a three-dimensional (3D) framework The compound 1 represents the first 3D "inverted Keggin" polyoxometalate modified by a transition-metal complex. Topologically, the 3D framework can be considered as an 8-connected net with a Schlafli symbol of 4(22).6(6). As far as we know, compound 1 is the highest connected uninodal network topology presently known for POM-based materials. The compound was characterized by its IR spectrum, UV-vis spectrum, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD) patterns. Remarkably, compound 1 exhibits photocatalytic activity for dye degradation under visible light irradiation and shows good stability toward visible-light photocatalysis.