The synthesis of monoperoxo-vanadium(V) complexes, [VO(O2)QL] (Q = 8-quinolinolate and L = EtOH, DMF, DMSO, or THF), and diperoxovanadates(V), A3[VO(O2)2(HPO4)].2H2O (A = K or NH4) are described. While the [VO(O2)QL] complexes have been synthesized from the reaction of V2O5 With H2O2 and a solution of 8-quinolinol in different donor solvents (L) at pH ca. 2, the oxodiperoxo(hydrophosphato) vanadate(V) dihydrates, A3[VO(O2)2(HPO4)].2H2O, have been prepared from the reaction of V2O5 with H2O2 and phosphoric acid at pH 6 of the reaction medium. The compounds have been characterized by chemical analyses, magnetic susceptibility, and molar conductance measurements, and by IR, laser Raman, H-1 NMR, and electronic spectroscopic studies. Evidence has been provided for triangularly bonded peroxide (O2(2-)) and coordinated heteroligands. The existence and stability of the complex [VO(O2)2(HPO4)]3- in solution have been ascertained from solution Raman spectroscopy and conductance measurements.