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

Abstract

The 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.

Extraction-Chromogenic Systems for Vanadium(V) Based on Azo Dyes and Xylometazoline Hydrochloride

“…This is evidenced by differences in the spectral characteristics and optimal pH intervals of existence of V(IV)-and V(V)−ARD complexes. 37,46,60 Furthermore, ADRs have been successfully used for V(IV)/V(V) speciation. 8,10,15,61 In this case, the main concern is to prevent the oxidation of V(IV) by the oxygen in air, which starts at ca.…”

“…The differences are explained by the possibility of interactions (H-bonding) between ADR and CIAR or between CIAR and the VO 2 group, 29 which is generally stable 26,31,32 but under certain conditions is prone to lose an oxygen atom. Moreover, V(V) is stereochemically flexible; [33][34][35] the same is true for ADRs which have many conformers 36 and can be tridentate, bidentate, and even monodentate ligands 37 depending on the environment.…”

Extraction-Chromogenic System for Cobalt Based on 5-Methyl-4-(2-thiazolylazo) Resorcinol and Benzalkonium Chloride

“…The following cationic reagents have been used as components of Co-PAR and Co-TAR ternary complexes: diphenylguanidine, 15 dicyclohexyl-18-crown-6, 17 tetradecyl(trihexyl)phosphonium chloride, 21 xylometazoline hydrochloride, 19 tributylammonium bromide, 22 tetraphenylarsonium chloride, 28,29 tetraphenylphosphonium chloride, 28,29 nitron, 30 tetrazolium salts, 27,[31][32][33] and quaternary ammonium salts. 16,18,20,[34][35][36] 5-Methyl-4-(2-thiazolylazo)resorcinol (MTAR) 37 is a TAR derivative that has been used in our laboratory for the liquid-liquid extraction of V IV,V [38][39][40][41][42] and Ni II . 43 Its interaction with Co II in water-ethanol medium has been studied by Kiryukhina.…”

Vanadium-Containing Anionic Chelate for Spectrophotometric Determination of Hydroxyzine Hydrochloride in Pharmaceuticals

“…The good extractability of the V(V)–HTAR–HZH ternary complex could be attributed to the effective hydrophobic envelope around the central V(V) ion and other hydrophilic regions. The bulkiness and spatial shape of both the ligand (HTAR) and the cation (HZH + ) are essential for this [ 27 , 34 , 35 ]. Apparently, only the V(V)–HTAR anionic complex possesses the needed structural features favoring its appropriate positioning relative to the cation.…”