A novel organic-inorganic hybrid nickel molybdenum(V) phosphate has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility. The structure consists of poly(oxomolybdophosphate) anions linked by both Ni-II cations and 4,4-bipyridine bridging ligands to form a three-dimensional open-framework structure with large cavities where the uncoordinated 4,4'-bipyridinium cations and lattice water molecules are located. This is the first example of an extended framework solid containing poly(oxomolybdophosphate) anions interconnected by both transition-metal complexes and organic moieties. Crystal data: (4,4'-H(2)bpy)[Ni(4,4'-bpy)(H2O)(2)Ni-0.5-Mo-6(OH)(3)O-12(HPO4)(4)]cente r dot 2H(2)O, orthorhombic, space group Pccn( No. 56), a = 27.745(2) angstrom, b = 16.158(1) angstrom, c = 22.819(2) angstrom, V = 10230.3(1) angstrom(3), and Z = 8.