Abstract

For a series of metal-ion sulfate solutions investigated, only In³⁺ showed Raman spectral evidence of association with SO₄⁼. The evidence consisted of the appearance in indium sulfate solutions of four new polarized lines in the Raman spectrum. Three of these were accounted for in terms of C_3v symmetry for the bound sulfate ion and the assignment thus was: v₁(A₁)=1125 cm^—1, v₂(A₁)=1000 cm^—1, v₃(A₁)=650 cm^—1. The fourth new line, at 255 cm^—1, was also present (at 270 cm^—1) in indium nitrate solutions and thus assigned to an In-O stretching mode. Raman intensity data, particularly in mixed indium sulfate—indium perchlorate solutions, verified the new species as an indium—sulfate complex; however, these data did not permit a decision between the presence of InSO₄⁺, In(SO₄)₂^—, or a mixture of the two. The fact that the 255 cm^—1 line was found to be highly polarized suggested that a linear In(SO₄)₂^— species might be of major importance. Finally, all indium solutions, even those with ClO₄^— as the only anion, showed a broad polarized band near 400 cm^—1 which probably resulted from hydrated In³⁺.