Dithizone and Its Oxidation Products: A DFT, Spectroscopic, and X-ray Structural Study

Abstract

Air oxidation of ortho-fluorodithizone resulted in the first X-ray resolved structure of a disulfide of dithizone, validating the last outstanding X-ray structure in the oxidation of dithizone, H(2)Dz, which proceeds via the disulfide, (HDz)(2), to the deprotonated dehydrodithizone tetrazolium salt, Dz. Density functional theory calculations established the energetically favored tautomers along the entire pathway; in gas phase and in polar as well as nonpolar solvent environments. DFT calculations using the classic pure OLYP and PW91, or the newer B3LYP hybrid functional, as well as MP2 calculations, yielded the lowest energy structures in agreement with corresponding experimental X-ray crystallographic results. Atomic charge distribution patterns confirmed the cyclization reaction pathway and crystal packing of Dz. Time dependent DFT for the first time gave satisfactory explanation for the solvatochromic properties of dithizone, pointing to different tautomers that give rise to the observed orange color in methanol and green in dichloromethane. Concentratochromism of H(2)Dz was observed in methanol. Computed orbitals and oscillators are in close agreement with UV-visible spectroscopic experimental results.

Effect of various solvents on the absorption spectra of dithizone and DFT calculations

“…The total energies calculated for the keto and enol forms indicate that the keto form is favored in the gas phase by 25.2 kJ/mol, consistent with previously published calculations [10]. The calculated spectra showed two absorption bands in the visible region for the keto form and one absorption band for the enol form.…”

“…The electronic absorption spectra of the compound were recorded in the 300-800 nm range and the results are shown in Table 1. The keto form of dithizone belongs to the longer wavelength band (620 nm) in the UV-Visible spectroscopy while the shorter wavelength band (450 nm) arises from the overlap of the keto and the enol forms [10]. The longer wavelength band was targeted for solvent-solute interaction studies, as it is unique to the keto form, and also shows pronounced shift with the solvent.…”

“…1. [10]. Dithizone has the ability to be both readily oxidized and reduced, as result of which the chemistry of dithizone is complicated [11].…”

(1,5-Diphenylthiocarbazonato-κS)trimethyltin(IV)

“…For the synthesis of dithizone, see: Pelkis et al (1957). For structural aspects of dithizone and its oxidation products and observed solvatochromism and concentratochromism, see: Von Eschwege et al (2011a). For related ligand and complex structures, see: Harrowfield et al (1983); Kong & Wong (1999); Herbstein & Schwotzer (1984); Fernandes et al (2002); Von Eschwege et al (2008); Laing et al (1971).…”

Zn(II)-concentration dependent Raman spectra in the dithizone complex on gold nanoparticle surfaces in environmental water samples

“…The energetic stabilities of various tautomers of H 2 Dz have been recently studied using density functional theory [8]. Raman spectra of H 2 Dz have been investigated on silver electrode and film surfaces [9,10].…”