Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H(2)bihyat) with (NaVO3)-O-V in aqueous solution followed by addition of either Ph4PCl or C(NH2)(3)Cl, respectively, gave the mononuclear vanadium(V) compounds Ph4P[(VO2)-O-V(bihyat)] center dot 1.5H(2)O (1) and C(NH2)(3)[(VO2)-O-V(bihyat)] (2). Treatment of (VOSO4)-O-IV center dot 5H(2)O with the ligand H(2)bihyat in methyl alcohol under specific conditions gave the oxo-bridged dimer [(V2O2)-O-V(mu(2)-O)(bihyat)(2)] (3). The structures for 1 and 3 were determined by X-ray crystallography and indicate that these compounds have distorted square-pyramidal arrangement around vanadium. The ligand bihyat(2-) is bonded to vanadium atom in a tridentate fashion at the pyridine-like nitrogen atom and the two deprotonated hydroxylamino oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms (Scheme 4), leads to very strong V-N bonds. The cis-[(VO2)-O-V(bihyat)](-) species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 3.3-11.0, as it was evidenced by H-1 and V-51 NMR spectroscopy and potentiometry. The high affinity of the H(2)bihyat ligand for the (VO2+)-O-V unit, its tridentate character, as well as its small size, paves the way for potential applications in medicine, analysis, and catalysis for the C(NH2)(3)[(VO2)-O-V(bihyat)] compound. The molecular structures, vibrational and electronic spectra, and the energetics of the metal-ligand interaction for compounds 1 and 3 have been studied by means of density functional calculations.