Formazan complexes

The IR bands in a number of nickel complexes of triaryl formazans have been assigned by Arnold and Schiele.415 A similar assignment of the electronic bands has been carried out.414 LCAO-MO calculations correlate well with these assignments417 and have been extended to include both inner ligand transitions as well as charge transfer bands and d—d transitions.418 EPR spectra have been used to study the nature of bonding in copper complexes of heterocyclic-containing formazans.419 Metal formazan complexes have also been studied by electrochemistry.283,398 420-422... 

Metal-Complex (Formazan) Dyes. The hydrazone from 2-carboxyphenylhydra-zine-4-sulfonic acid and benzaldehyde is suspended in water and then dissolved by adding aqueous sodium hydroxide to obtain pH 6.5 -7.0. This solution is added to the aqueous diazonium salt solution obtained from a typical aqueous diazotiza-tion of 4-(2-sulfooxyethylsulfonyl)-2-aminophenyl-6-sulfonic acid. The mixture is then dripped into an aqueous solution of copper sulfate, while the pH is maintained with soda at 5.5 - 6.5. After complete coupling the pH is adjusted to 1 with concentrated hydrochloric acid. The strongly acidic solution is then neutralized with alkali to pH 5.5. The copper - formazan complex is salted out along with sodium chloride, filtered, washed with dilute aqueous sodium chloride solution, and dried. A dark powder results which gives a dark blue solution in water. It consists of an electrolyte-containing powdered sodium salt of the acid 25 ... 

Wool and Polyamide Dyes. Water-soluble formazan complexes having sulfonamide, alkylsulfonyl, or sulfonic acid groups possess a high affinity to nitrogen-containing fibers. As with acid dyes, they can be used to dye wool and polyamide in neutral to weakly acid baths. Commercial dyes of this type are C.I. Acid Blue 267 and 297, and the 1 2 cobalt complex C.I. Acid Black 180, 13710 [11103-91-6] (29). 

A new field in which to apply formazan complexes has been opened up by a patent which utilized, in wool dyeing, the copper complexes of formazans containing hydroxyl or carboxyl groups in the ortho position. 

Oxidation of formazans with a wide range of oxidizing agents leads to 2,3-disubstituted tetrazolium salts. Recently, oxidations with cupric acetate and cobalt chloride have led to mixtures of metal-formazan complexes and tetrazolium salts arising from competing reactions in which the balance depended on the substituents present in the formazans.462 Reduction of 1,4,5-trisubstituted tetrazolium iodides with NaBH has been used to prepare A2-tetrazolines.463 A similar attempted reduction of 1,3,5-trisubstituted tetrazolium salts gave no reaction.463... 

The MIC value which is defined as the minimum concentration of an antimicrobial that is able to restrict the growth of microbial after whole night incubation have been determined by broth dilution method. Initial concentration of the nanocomposites for the test is taken as 10 mg/ml and diluted twice in each time up to a concentration of 0.0195 mg/ml. Nanocomposites with different concentrations have been subjected to E. coli and S. aureus to investigate the value of MIC. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoIiiun bromide) is added to the solution after 16 h incubation in Luria Berteni media in 96 well microtiter plate and incubated for 45 min in dark. Live bacterial cells which are capable to produce succinate dehydrogenase (enzyme) which reacts with MTT and forms formazan complexes with purple appearance. So the well having minimum concentration of sample where the complex does not form i.e. which does not appear purple is considered as the MIC value of the compound and is presented in the Table 7. It is observed that the MIC value of the nanocomposites decreases with the increase in Ag-NPs concentration in the nanocomposites and is minimum in the case of nanocomposites with 15 wt% of Ag-NPs. 

Another class of metal complex dyes is derived from the formazan stmcture. These dyes are appHed to wool and nylon from a neutral or weakly acidic dyebath analogous to the 2 1 premetallized OjO -dihydroxyazo complexes. The bluish-gray dye Cl Acid Black 180 [11103-91-6] (61) (Cl 13710) is a 2 1 cobalt complex of the formazan type. 

Formazan, l-(2-hydroxophenyl)-3,5-diphenyl-copper(II) complexes dyes, 6, 81... 

Formazan, l-(2-hydroxy-5-suIfophenyl)-3-phenyl-5-(2-carboxyphenyl)-zinc detection, 6, 83 Formazans cobalt complexes dyes, 6, 81 metal complexes bidentate, 6, 78 color photography, 6,111 dyes, 6, 77 tetradentate, 6, 81 tridentate, 6, 79... 

Electrochemical methods have been used extensively to elucidate the mechanism of reduction of tetrazolium salts. In aprotic media, the first step is a reversible one-electron reduction to the radical 154 as confirmed by ESR spectroscopy.256,266 As shown in Scheme 26, this radical can then disproportionate to the tetrazolium salt and the formazan anion (166) or take up another electron to the formazan dianion (167). The formation of the dianion through a direct reduction or through the intermediate tetrazolyl anion (168) has also been proposed.272-28 1,294 In aqueous solutions, where protonation/deprotonation equilibria contribute to the complexity of the reduction process, the reduction potentials are pH dependent and a one-electron wave is seldom observed. 

The chemistry of tetrazolium thiolates and other mesoionic tetra-zoliums has been extensively reviewed.297,298 Tho ugh there are no reports of the chemical reduction of thiolates to formazan-like structures, the polarographic reduction of the complex betaines (146) to formazans has been reported.655... 

The physical and chemical properties of formazans have been reviewed in detail.1,2 In this discussion only those properties that directly or indirectly affect the choice of a tetrazolium salt as a leuco dye will be discussed. Spectral, acid—baseyedox, and metal complexing properties will be stressed. 

Unsymmetrically substituted formazans form a complex mixture of valence tautomers and geometric isomers with different conformations. The tautomerism is further complicated when substituents on the aryl ring are... 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

A variety of complexes, e.g., 224 and 225, can be formed from the tetradentate formazans.384,385,388 396 Tetradentate formazans containing heterocycles, e.g., 226 and 227, also form metal complexes.385... 

The bulk of the literature on the coordination chemistry of formazans deals with complexes of copper, nickel, cobalt, and chromium. 

Other transition metals have received much less attention. Complexes of palladium and 2-amino-phenyl-containing formazans have been reported.397 Mercury complexes of tridentate formazans have been studied.398 Silver complexes of tridentate benzothiazolyl-containing formazans have also been studied.399 Recently, alkali and alkaline earth metals have been the subject of many studies. Formazans such as 228 and 229 as well as the macrocyclic 204 have received considerable attention as metal-specific analytical reagents.400-41 1... 

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

Formazans and their metal complexes are used as textile dyes by direct application. The in situ reduction of tetrazolium salts has not been used to introduce the dyes to their substrates. Treatment with triaryl mono and bis tetrazolium salts followed by a reducing agent such as ascorbic acid or thioglycolic acid has been claimed as a method of introducing formazans as permanent hair dyes.641 There are some references to their use as therapeutic agents.642 544... 

There are bi-, tri-, and tetradentate formazan dyes7 but only the tetradentate copper complex formazan dyes have found use as commercial products. The dye Cl Reactive Blue 160, of generic structure (41), is a representative example. Because of the intensity of their colors, the metal complex formazan dyes have also found application in analysis. Thus, the dye (42) detects zinc at a concentration of 1 part in 50 million.31... 

An appropriate ion-specific electrode was found to provide a convenient, precise and relatively inexpensive method for potentiometry of copper(II) ion in copper-complex azo or formazan dyes. Copper(II) ion in copper phthalocyanine dyes can be quantified after anion exchange. Twelve commercial premetallised dyes evaluated using this technique contained copper(II) ion concentrations in the range 0.007 to 0.2%. Thus many copper-complex direct or reactive dyes are likely to contribute low but possibly significant amounts of ionic copper to textile dyeing effluents [52]. 

---