Peroxo heteroligand vanadates(V): synthesis, spectra-structure relationships, and stability toward decomposition

Abstract

Effect of heteroligands (L) on the properties of vanadium peroxides was investigated by preparing a number of peroxovanadium complexes, which were characterized by analysis, IR, UV/V and NMR spectra. X-ray structures for some were obtained. The vanadates(V) contain the cation M(I) = Na, K, NH4, Rb or Cs. Diperoxo complexes include M(I)[VO(O2)2 L], where L = dipyridyl, o-phenanthroline; M(I)3[VO(O2)2(C2O4)]; K2[(nicotinic acid)[VO(O2)2]2]H2O;M(I)4[O[VO(O2)2]2cystine]2H2O; H4[O[VO(O2)2(adenine)2)2]2H2O; and K2H2[O[VO(O2)2(adenosine)]2] 2H2O. Monoperoxo vanadates(V) correspond to the formula M(I)2[VO(O2)L]2 for L = citrate and malate; M(I)2[VO(O2)L] for L = nitrilotriacetate; M(I)[VO(O2)L] for L = iminodiacetate, tartrate and EDTA; and [HVO2(O2)(adenosine)]2H2O. Syntheses of these heteroligand peroxovanadium compounds are sensitive to pH, temperature and the concentration of the components. The stability towards decomposition in solid state, mother-liquid and pure water solutions depends upon the heteroligand. Characteristic (V = O) and (O-O) stretching frequency bands in IR can be correlated with the corresponding bond lengths and the [peroxo approximately V(V)] charge transfer bands in UV/V spectra. Intramolecular one-electron transfer in peroxo vanadates(V) can trigger the generation of radicals, and its dependency upon the nature of the heteroligand is discussed.