A novel vanadium(V) phosphate and the arsenate analogue, [(VO2)(2)(4,4'-bpy)(0.5)(4,4'-Hbpy)(XO4)](H2O)-H-. (X = P, As; bpy = bipyridine), have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. They are the first structurally characterized compounds in the vanadium(V)/4,4'-bpy/phosphate (or arsenate) systems. The two compounds are isostructural and crystallize in the triclinic space group P (1) over bar (No. 2) with a = 7.9063(3) Angstrom, b = 10.2201(4) Angstrom, c = 12,1336(5) Angstrom, alpha = 113.4652(7)degrees, beta = 95.7231(7)degrees, gamma = 94.4447(7)degrees, and Z= 2 for the phosphate, and a = 7.8843(6) Angstrom, b = 10.3686(7) Angstrom, c = 12.2606(9) Angstrom, alpha = 113,464(1)degrees, beta = 95.560(1)degrees, gamma = 94.585(1)degrees, and Z = 2 for the arsenate. The structure consists of phosphate-bridged vanadium(V) double chains linked through 4,4'-bpy ligands to form a sheet with the monoprotonated 4,4'-Hbpy(+) ligand being coordinated to the metal atom as a pendent group. The H-1 MAS NMR spectrum exhibits four resonances at 14,2, 9.5, 7.2, and 3.7 ppm with an intensity ratio close to 1:6:6:2, corresponding to three different types of protons in 4,4'-bpy and 4,4'-Hbpy, and one type of protons in H2O. The peak at 14.2 ppm can be assigned to the proton bonded to the pyridine nitrogen atom, which confirms the presence of 4,4'-Hbpy(+).