Specific features of tetranitrotetrazolium blue chloride as an extraction reagent for iron(III)

A liquid-liquid extraction-chromogenic system containing Fe(III), 4-(2-thiazolylazo)resorcinol (TAR), [3,3’-(3,3’-dimetoxy-4,4’-biphenylene)bis[2,5-di(4-nitrophenyl)-2H-tetrazolium] chloride (tetranitro-tetrazolium blue chloride, TNBT), water, and chloroform was studied and compared with similar systems containing such ditetrazolium salts (DTS), as neotetrazolium chloride (NTC), blue tetrazolium chloride, and nitro blue tetrazolium chloride. The results show that the complex formed in the Fe(III)–TAR–TNBT system is of different composition (1 : 3 : 2 vs. 1 : 2 : 1) and has better extraction-spectrophotometric characteristics (fraction extracted is 98.6 % and molar absorptivity, 7.8 × 10⁴ dm³ mol^–1 cm^–1 at λ = 495 nm). The proposed formula of the complex is (TNBT⁺)[Fe^III(TAR^2–)₂]·{(TNBT⁺)(HTAR^–)}, where TNBT is in the monocationic form. The geometry optimization for TNBT and NTC–the DTS, which does not contain nitro- and methoxy groups, was performed by the Restricted Hartree–Fock (RHF) method with the 3-21G* basis set. The obtained results (ground-state structures and total atomic charges) for TNBT, TNBT⁺, TNBT²⁺, NTC, and NT²⁺ were compared and discussed.