Complex formation in a liquid-liquid extraction-chromogenic system for vanadium(IV)

• Published in: Open Chemistry Vol. 17; no. 1; pp. 599 - 608
• Main Authors: Gavazov, Kiril B., Delchev, Vassil B., Milcheva, Nikolina P., Toncheva, Galya K.
• Format: Journal Article
• Language: English
• Published: De Gruyter 01-01-2019
• Subjects: azo dye; HF and DFT calculations; hydrogen bond; ternary complex; tridentate/monodentate coordination
• ISSN: 2391-5420; 2391-5420
• DOI: 10.1515/chem-2019-0071

The azo dye 4-(2-thiazolylazo)orcinol (TAO) and the cationic ion-pair reagent 2,3,5-triphenyl-2
-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
=544 nm,
=1.75×10
dm
mol
cm
and Log
=4.1. The ground state equilibrium geometries of the possible monoanionic V
-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 V
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 V
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.