Raman Spectral Studies of Cadmium–Nitrite Interactions in Aqueous Solutions and Crystals

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Abstract
Raman spectra of aqueous solutions containing Cd2+ and NO2− clearly reveal the presence of solvated nitrite ion and of complexes. A band at 861 cm−1 is characteristic of the latter. The free nitrite concentration was measured from the intensity of the 817 cm−1 line and the average ligand number was evaluated for solutions with composition prescribed by the mole-ratio method. Four cumulative formation constants were deduced: β1 = 61.6; β2 = 993; β3 = 2390; β4 = 1899. Evidence that nitrite chelates Cd2+ through the two oxygen atoms is presented. The diagnostic spectral evidence consists of a high intensity, high frequency deformation mode and low intensity N—O stretching Raman bands with frequencies almost identical to those of the solvated nitrite ion. Data are also presented for solid Cd(NO2)2 and Kx−2Cd(NO2)x(x = 3,4,5).

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