Abstract
The complex formation between the anionic chelate of molybdenum(VI) with the bidentate ligand of 3,5-dinitrocatechol (3,5-DNC) and its ion-association with the cation of 2,3,5-triphenyl-2?-tetrazolium chloride (TTC) in the liquid-liquid extraction system Mo(VI)?3,5-DNC?TTC?H2O?CHCl3 were studied by spectrophotometry. The validity of Beer's law was checked and some analytical characteristics of the system were calculated under the optimum conditions for the chelate formation and extraction. The effect of various co-existing ions and reagents on the process of chelate formation and ion-association was investigated. The molar ratio of the components in the ion-associated complex Mo(VI)-3,5-DNC-TTC was determined by independent methods. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized by the following equilibrium constants: association constant, distribution constant, extraction constant and recovery factor. Based on this, a reaction scheme, a general formula and a structural formula of the complex were suggested.
Highlights
The acidity of the aqueous phase influences the extraction of the anionic chelate Mo(VI)‒3,5-DNC into the organic phase in the form of ion-associate with the tetrazolium cation of tetrazolium chloride (TTC)
The equilibria of the complex formation of the anionic chelate of molybdenum(VI) with the bidentate ligand of 3,5-dinitrocatechol (3,5-DNC) and its extraction with the cation of 2,3,5-triphenyl-2Н-tetrazolium chloride (TTC) in the form of an ion-associated complex in the liquid-liquid extraction system Mo(VI)‒3,5-DNC‒TTC‒ H2O‒CHCl3 was studied by spectrophotometry
From the analytical characteristics of the extraction system Mo(VI)‒3,5-DNC‒TTC‒ H2O‒CHCl3, it can be concluded that the ion-associate formed between the anionic chelate of Mo(VI)‒3,5-DNC and the monotetrazolium cation allows determinations of Mo(VI) with a high sensitivity
Summary
The molybdenum is a transition metal with rich coordination chemistry, it occurs in various oxidation states, coordination numbers and geometries.[1,2,3] Molybdenum(VI) forms complexes with various organic ligands, such as polyphenols and their functional derivatives, polyhydroxycarboxylic acids, aminopolycarboxylic acids, hydroxamic acids, amines (primary, secondary and ternary), 8-hydroxyquinoline and its derivatives, aldehyde hydrazones, oximes, β-diketones, fluorones, hydroxyazodyes, biomolecules (chitosan, chitin, D-glucosamine, L-alanine, L-phenylalanine).[4,5,6,7,8,9,10,11,12,13,14,15,16,17] Molybdenum(VI) complexes with bidentate ligands, containing [S,S], [S,O], [S,N] donor atoms, like toluene-3,4-dithiol, 2-mercaptophenol, 2-aminothiophenol, ethane-1,2-dithiol, dithiooxamide, 2-thiopheno-carboxamide, were obtained and structurally characterized.[18]. 2020, 67, 594–601 with N-, S- and O-containing donor atoms and with the participation of mono- and ditetrazolium cations are a special scientific research field of the chemistry of the coordination compounds. It is up-to-date topic, as a theoretical background for the preparation of novel ion-associated complexes, but mainly due to the possibility for their application in the Analytical Chemistry for determination of various metals in natural, industrial, pharmaceutical and biological samples, addressing in such a way a number of ecological issues. The presence of a quaternary nitrogen atom in the molecules of the tetrazolium salts determines the ability to form ionic associates in the aqueous phase without protonation, as opposed to the amines.[22,32,33]
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