Oxovanadium complexes aqueous solution

ESR spectra, 2, 511 Oxovanadium(V) complexes aqueous solution, 3,1026 Oxyanions coordinated... 

L — maltolate the coordination environment of the vanadium in K[V02(malt)2] H2O is approximately octahedral, the two 0x0 ligands being in cis positions. [K(H20)e] units link adjacent vanadium(V) complex anions to give a chain structure 166). The main products of aerobic oxidation of [V O(dmpp)2l in aqueous solution are [V02(dmpp)] and [VOo(dmpp)2]. High pH favors these V products, whereas at low pH V species predominate 171). Vanadium(V) also forms a VO(OR)(malt)2 series, readily prepared from ammonium vanadate, maltol, and the appropriate alcohol in a water-alcohol-dichloromethane medium 172), and 3-hydroxy-4-pyridinonate analogues V0(0R)L2 on oxidation of their oxovanadium(IV) precursors in solution in the appropriate alcohol ROH 168). 

Good evidence for the formation of dimeric 4,4, 4",4 "-tetrasulphophthalo-cyanine oxovanadiumtiv) species in HjO-DMF solutions has been obtained from e.s.r. spectra, and the metal centres are estimated to be 450 pm apart. In aqueous solution, although dimers are present, most of the oxovanadium(iv) complexes are polymerized, and in DMF solution substantial amounts of monomer exist. Stability constants for the formation of 1 1 complexes between pyridine and some oxovanadium(iv)-2,4-disubstituted deuteriopor-phyrin dimethyl esters have been determined in chloroform solution at 25 °C. Magnetic and spectroscopic evidence suggest the presence of an electronic interaction between centres in these compounds. 

Ghiron, A.F. and R.C. Thompson. 1990. Comparative kinetic study of oxygen atom transfer reactions of diperoxo and monoperoxo complexes of oxovanadium(V) in aqueous solution. Inorg. Chem. 29 4457-4461. 

NMR spectroscopy can also be used to determine the formation constants of various complexes. We illustrate this by quantificating the distribution of vanadate oligomers in aqueous solution by 51V NMR spectroscopy. Moreover, the chemical shifts are very sensitive to protonation of the oxovanadium species, and 51V spectra can provide information on the specific protonation state of the anions in solution. 

Dessi A, Micera G, Sauna D. 1993. EPR investigation of the oxovanadium(IV) complexes formed by the tripeptide glutathione and some related ligands in aqueous solution. JIrtorgBiochem 52 275-286. 

---