A mixed-valence vanadium phosphate, NH4[(V2O3)2(4,4′-bpy) 2(H2PO4)(PO4)2] ·O.5H2O, has been synthesized under hydrothermal conditions and structurally characterized by single-crystal x-ray diffraction. It crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.6354(8) Å, b = 9.9786(6) Å, c = 23.369(1) Å, β = 92.713(1)°, and Z = 4 with R1 = 0.0389. The structure consists of dimers of edge-sharing vanadium(IV,V) octahedra that are connected by corner-sharing phosphate tetrahedra to form layers in the ab-plane, which are further linked through 4,4′bipyridine pillars to generate a 3-D framework. Magnetic susceptibility confirms the valence of the vanadium atoms. The 31P MAS NMR spectrum shows a resonance centered at 80 ppm with a shoulder at ca. 83 ppm in an intensity ratio close to 1:2, which correspond to two distinct P sites. The observed large downfield 31P NMR shifts can be ascribed to magnetic exchange coupling involving phosphorus atoms. The unpaired electron spin density at the phosphorus nucleus was determined from variable-temperature 31P NMR spectra. The 1H MAS NMR spectrum was fitted to six components in accordance with the structure as determined from x-ray diffraction.