Abstract
AbstractThe azo dye 4-(2-thiazolylazo)orcinol (TAO) and the cationic ion-pair reagent 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) were examined as constituents of a water-chloroform extraction-chromogenic system for vanadium(IV). The effects of TAO concentration, TTC concentration, pH and extraction time were examined. Under the optimum conditions the extracted complex has a composition of 1:2:1 (V:TAO:TTC). The absorption maximum, molar absorptivity and constant of extraction were determined to be λmax=544 nm, ε544=1.75×104 dm3 mol–1 cm–1 and Log Kex=4.1. The ground state equilibrium geometries of the possible monoanionic VIV-TAO 1:2 species were optimized by the HF method using 3-21G* basis functions. Their theoretical time dependent electronic spectra were simulated and compared with the experimental spectrum. The best fit was obtained for the structure in which one of the TAO ligands is tridentate, but the other is monodentate (bound to VIV through the oxygen which is in the ortho-position to the azo group) and forms a hydrogen bond N–H...O=V through its protonated heterocyclic nitrogen. Based on this unusual structure, which can explain some peculiarities of the complex formation between VIV and commonly used azo dyes, the ground state equilibrium geometry of the whole ternary 1:2:1 complex was computed at the HF and BLYP levels.
Highlights
Vanadium occupies position 23 in the periodic table
Absorption spectra of VIV–the experimental conditions: [VIV(OH) (TAO)–triphenyl-2Htetrazolium chloride (TTC) extracts in the same solvent are shown in Figure 2, curves 1–3
The principal complex formed in the liquid-liquid extraction-chromogenic system VIV-TAO-TTC has a composition of 1:2:1 and can be represented by the formula (TT+)[VO(HNTAO)(TAO)]
Summary
Vanadium occupies position 23 in the periodic table. It is the fifth most abundant transition element in the Earth’s crust and has applications in many industries. Various hazards are associated with elevated concentrations of vanadium in the environment [3]. Health disorders can arise from vanadium deficiency [2, 4]. The window between beneficial and toxic action of this element is not well defined and depends on many factors, including the oxidation state. Uncertainties in the correlation between toxicity–oxidation state and toxicity–ligand system [8,9,10], along with vanadium’s stereochemical flexibility [11, 12] define the necessity for thorough investigations on its coordination chemistry. It is important to develop reliable methods for determining VIV and VV in their joint presence [13,14,15]
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