Abstract
The isomorphic series of double sulfites with empirical formula Cu2SO3.MSO3.2H 2O (where M is Cu, Fe, Mn, or Cd) have been prepared from the Cu(II) replacement by transition metal ions such as Mn(II), Fe(II) and Cd(II) ions in Chevreul's salt, Cu2SO3.CuSO3.2H 2O. As a consequence, the isomorphic species present distinct colors. Molecular modeling calculations were carried out for the dimeric [CuI2(SO3) 2(SO3)2]6- center. The electronic spectra of the Chevreul's salt consist of a charge-transfer band around 425 nm associated with the [CuI2(SO3) 2(SO3)2]6- chromophore and two ligand field transitions at 785 and 1000 nm involving the Jahn-Teller splitting of the Cu(II) levels. An additional intervalence-transfer band, responsible for its characteristic red color, can be found at 500 nm. The replacement of the Cu(II) ions for Fe(II), Mn(II) and Cd(II) does not eliminate the absorption band at 425 nm, supporting its assignment as a charge-transfer transition centered on the Cu(I) sites; while the original band at 500 nm disappears, in agreement with its intervalence transfer nature.
Highlights
The first known mixed valence sulfite complex, CuI2SO3.CuIISO3.2H2O, was prepared by M
The electronic spectra were recorded on a Guided Wave spectrophotometer, model 260, equipped with a Wand bundle probe for in situ reflectance measurements
The high energy band at 425 nm seems to be a common feature of the Chevreul’s salt derivatives and it would be better ascribed to a transition in the Cu(I)-sulfite chromophore, rather than to an intervalence transfer transition
Summary
The first known mixed valence sulfite complex, CuI2SO3.CuIISO3.2H2O, was prepared by M. Up to the present time, there is a complete lack of information about the electronic interactions between the constituents of Chevreul’s salt derivatives, especially concerning the types of electronic transitions responsible for their different colors. For this reason, this subject is focused in this paper, with emphasis on the theoretical evaluation of the chargetransfer bands in the Chevreul’s salt. Mixtures of copper and manganese, copper and iron or copper and cadmium sulfate solutions (see compositions in Table 1) were saturated with sulfur dioxide gas at room temperature to give solutions with pH of approximately 1. A more detailed account on their syntheses can be found elsewere.[4,5]
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