Formazan triaryl

Though formazans can be protonated, there are no reports of isolation of formazan cations. The study of the basicity of formazans is complicated by the fact that exposure to acid can lead to irreversible chemical changes. Recently, the protonation of the triaryl formazan 194 with perchloric acid in aprotic solvents has been studied spectroscopically. In this a hypso-chromic shift is observed and is more pronounced when X is an electron-donating substituent. Thus, the shift is 33, 14, and 73nm when X is hydrogen, /Mnethoxy, and w-nitro, respectively.337... 

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... 

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... 

Triaryl-tetrazolium-chloride geben beim photolytischen Zerfall zunachst Triaryl-formazane, die unter Belichtung zu Dibenzopyridazino-[l,2-b]-tetrazolium-cbloriden cyolisieren1-4 ... 

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