Complex Formation in a Liquid-Liquid Extraction System Containing Vanadium(IV/V), 2,3-Dihydroxynaphtahlene and Thiazolyl Blue

Abstract

Liquid-liquid extraction systems for V^IV/V containing 2,3-dihydroxynaphtahlene (DN) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (thiazolyl blue, MTT) were studied. The optimum conditions for V^IV and V^V extraction were found. V^IV is extracted in chloroform as a 1:2:2 complex (V:DN:MTT) with l_max = 570 nm and e₅₇₀ = 2.9´10⁴ dm³ mol^–1 cm^–1. However, this wavelength was found unsuitable for precise spectrophotometric measurements due to time dependent absorbance changes. V^V forms predominantly a 1:1:1 complex with l_max = 335 nm. The calibration graph for this oxidation state is linear in the range of 0.06–1.5 mg cm^–3. The molar absorptivity, Sandell’s sensitivity and limit of detection were calculated to be 1.6 ´ 10⁴ dm³ mol^–1 cm^–1, 3.2 ng cm^–2 and 0.02 mg cm^–3, respectively. The ground-state equilibrium geometries of the anionic parts of the extracted ion-associates, [V^IVO(DN^2-)₂]^2-and [V^VO₂(DN^2-)]^-, were optimized  at the BLYP/6-31++G* level of theory.