Vanadium(IV,V) complexes of D-saccharic and mucic acids in aqueous solution.
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 degrees 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)(2)L(2)H(x)](x=-2 and -4). Joint evaluation of the pH-potentiometric and (51)V 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).
Dornyei
Agnes
A
Department of Chemistry, University of Sassari, Via Vienna 2, I-07100, Sassari, Italy.
Garribba
Eugenio
E
Jakusch
Tamas
T
Forgo
Peter
P
Micera
Giovanni
G
Kiss
Tamas
T
D005937:Glucaric Acid / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D011199:Potentiometry; D012996:Solutions; D013053:Spectrophotometry; D013400:Sugar Acids / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
D012996:Solutions; D013400:Sugar Acids; D014638:Vanadates; C000090:galactaric acid; D005937:Glucaric Acid