Polysulfide Anions. 1. Structure and Vibrational Spectra of the S22- and S32- Anions. Influence of the Cations on Bond Length and Angle

In a comprehensive study of the M2Sn and M‘Sn alkali (M) and alkaline-earth (M‘) polysulfides, the alkali polysulfides K2S2, Na2S3·NH3, and K2S3 have been prepared by reaction of the metal with sulfur in liquid ammonia and subsequent heat treatments. Their Raman spectra have been analyzed in relation to their known X-ray structures, and that of BaS3 has been revisited. The structure of K2S2 seems intermediate in the M2S2, M‘S2 series since it has two slightly different anions in the unit cell. As for Na2S2, K2S2 has two α and β phases but with a much higher transition temperature ∼310 °C. These results, and those of the literature, allow the S22- bond length to be related to the variation of its electronic structure with the cation electric field. The results obtained for the M2S3 and M‘S3 polysulfides, and those of the literature, show the existence of a low- and a high-temperature phase for K2S3 as for the other M2S3 compounds. The S32- anion geometry, as for S22-, is directly related to the cation elec...