Extractive Spectrophotometric Determination and Theoretical Investigations of Two New Vanadium(V) Complexes

Two new vanadium (V) complexes involving 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR) and tetrazolium cation were studied. The following commercially available tetrazolium salts were used as the cation source: tetrazolium red (2,3,5-triphenyltetrazol-2-ium;chloride, TTC) and neotetrazolium chloride (2-[4-[4-(3,5-diphenyltetrazol-2-ium-2-yl)phenyl]phenyl]-3,5-diphenyltetrazol-2-ium;dichloride, NTC). The cations (abbreviated as TT(+) and NTC(+)) impart high hydrophobicity to the ternary complexes, allowing vanadium to be easily extracted and preconcentrated in one step. The complexes have different stoichiometry. The V(V)–HTAR–TTC complex dimerizes in the organic phase (chloroform) and can be represented by the formula [(TT(+))[VO(2)(HTAR)]](2). The other complex is monomeric (NTC(+))[VO(2)(HTAR)]. The cation has a +1 charge because one of the two chloride ions remains undissociated: NTC(+) = (NT(2+)Cl(−))(+). The ground-state equilibrium geometries of the constituent cations and final complexes were optimized at the B3LYP and HF levels of theory. The dimer [(TT(+))[VO(2)(HTAR)]](2) is more suitable for practical applications due to its better extraction characteristics and wider pH interval of formation and extraction. It was used for cheap and reliable extraction–spectrophotometric determination of V(V) traces in real samples. The absorption maximum, molar absorptivity coefficient, limit of detection, and linear working range were 549 nm, 5.2 × 10(4) L mol(−1) cm(−1), 4.6 ng mL(−1), and 0.015–2.0 μg mL(−1), respectively.