Dörnyei, Ágnes and Garribba, Eugenio and Jakusch, Tamás and Forgó, Péter and Micera, Giovanni and Kiss, Tamás (2004) Vanadium(IV,V) complexes of D-saccharic and mucic acids in aqueous solution. Dalton Transactions, Vol. 2004 (12), p. 1882-1891. eISSN 1477-9234. Article.
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The vanadium(IV,V) complexes formed with two aldaric acids (D-saccharic or D-glucaric acid, and mucic or galactaric acid) in aqueous solution were characterised by employing pH-potentiometry, EPR, multinuclear NMR and UV-VIS spectroscopy. The stoichiometry and stability constants of the complexes formed were determined at 25 °C and ionic strength I = 0.2 mol dm−3 (KCl). The spectral measurements revealed that vanadium(IV,V) coordinates first at the terminal COO− functions, forming mononuclear complexes. At pH > 3, through the metal ion-induced deprotonation and coordination of the neighbouring alcoholic functions, (COO−, O−) coordinated dinuclear complexes are formed, which predominate in the pH range 4–8. In the basic pH range, the ligand molecules are displaced and binary metal hydroxo and oxo complexes are present. EPR measurements at room temperature and at 140 K proved that formation of the VO(IV) dimers is more enhanced at room temperature, but at 140 K their dissociation is favoured. An interesting pH-dependent cis–trans isomeric equilibrium was assumed and analysed by EPR and molecular modelling in the case of the complexes [(VO)2L2Hx] (x = −2 and −4). Joint evaluation of the pH-potentiometric and 51V NMR measurements revealed that both aldaric acids are able to bind an excess of vanadium(V), through the formation of oligomeric 2 : 1 and 3 : 2 species, besides the 2 : 2 species formed with VO(IV).
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