Polysulfide anions II: Structure and vibrational spectra of the S-4(2-) and S-5(2-) anions. Influence of the cations on bond length, valence, and torsion

The influence of the cations on bond length, valence, and torsion angle of S-4(2-) and S-5(2-) anions was examined in a series of solid alkali tetra- and pentasulfides by relating their Raman spectra to their known X-ray stru ctures through a force-field analysis. The IR and Raman spectra of BaS4. H2 O and the Raman spectra of (NH4)(2)S-4. nNH(3), gamma-Na2S4, and delta-Na2S 5 are presented. The similarity of spectra of gamma-Na2S4 with those of BaS 4. H2O suggests similar structures of the S-4(2-) anions in these two compo unds with a torsion angle smaller than 90 degrees. The variations of SS bon d length, SSS valence angle, and dihedral angle of S-n(2-) anions are relat ed to the polarization of the lone pair and electronic charge of the anion by the electric field of the cations. A correlation between the torsion ang le and the SSS valence angle is shown as that previously reported between t he length of the bond around which the torsion takes place and the dihedral angle value. These geometry changes are explained by the hyperconjugation concept and the electron lone-pair repulsion.