Vibrational spectra of the ethylenediammonium ion in crystals

The IR and Raman spectra of three isotopic varieties of the ethylenediammonium ion in the tetrachlorocadmate(II) have been measured. It is shown that the ion assumes the centrosymmetric trans conformation in this salt. A complete vibrational assignment has been proposed for the observed fundamentals. Certain assignments for related compounds in the literature are modified. The spectra of the ion in the hexachloroplatinate(IV) and hexachlorostannate(IV) have also been obtained; compared to these two compounds hydrogen bonding in the tetrachlorocadmate is appreciable. Combination bands observed in the 2100-1800 cm^?1 region of the IR and Raman spectra of compounds containing the C-NH₃⁺ grouping are discussed and assignments are suggested for those observed in ethylenediammonium salts.