 ISSN 0235-7216 ISSN 2424-4538 (online) |
2010 m. Nr. 2-4 Ternary complexes of niobium(V) with nitroderivatives of catechol and tetrazolium salts. Extraction-spectrophotometric investigations
The formation and solvent extraction of new ion-association complexes between anionic chelates of niobium(V) with nitroderivatives of catechol {NDC: 3,5-dinitrocatechol (3,5-DNC) and 4-nitrocatechol (4-NC)} and tetrazolium cations {2,3,5-triphenyl-2H-tetrazolium (TT+) and 3,3’-[3,3’-dimetoxy(1,1’-biphenyl)–4,4’-diyl]-bis[2,5-diphenyl–2Htetrazolium] (Blue Tetrazolium, BT2+)} were studied. Niobium(V) forms two complexes with 4-NC and BT2+ and one complex with 3,5-DNC and TT+ with suggested formulae (BT2+) [NbO(OH)(4-NC)2] (I), (BT2+)3[NbO(4-NC)3]2 (II), and (TT+)2[NbO(OH)(3,5-DNC)2] (III). The optimum conditions for the extraction of II and III (organic solvent, extraction time, acidity of the aqueous phase, concentration of reagents), some key constants {association constant (β), constant of distribution (KD), extraction constant (Kex)} and analytical characteristics were determined. The molar absorptivities of II and III were calculated to be ε'415 = 4.6 × 104 L mol–1 cm–1 and ε'400 = 2.5 × 104 L mol–1 cm–1, respectively. Beer’s law was obeyed for Nb(V) concentrations ranging from 0.42 to 1.6 μg/mL (II) and 0.51 to 2.3 μg/mL (III). Keywords: niobium, liquid–liquid extraction, spectrophotometry, nitrocatecholates, tetrazolium salts |
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