Schwingungsspektren und Normalkoordinatenanalyse der Chloro-Bromo-Osmate(IV), [OsCl„Br6-n]2-, n = 0-6 / Vibrational Spectra and Normal Coordinate Analysis of Chloro-Bromo-Osmates(IV), [OsCl„Br6-n]2-, n = 0-6

Abstract

The IR- and Raman spectra of the ten chloro-bromo-osmates(IV) [OsCl„Br6-n]2-, n = 0-6, including the geometrical isomers for n = 2, 3, 4 have been recorded at low temperature (80 K). The vibrational spectra of these complexes are completely assigned according to point groups Oh, D4h, C4v, C3v and C2v, supported by normal coordinate analyses based on a general valence force field. Due to the stronger trans-influence of Br as compared to Cl, in all asymmetric Cl—Os—Br axes the Os—Br bonds are strengthened and the Os—Cl bonds are weakened, indicated by valence force constants for Os— Br approximately 6% higher, for Os—Cl 6% lower, as compared with the values calculated for symmetrical Br—Os—Br and Cl-Os-Cl axes, respectively. The significantly stronger interaction between opposite bonds is revealed by the stretching interaction constants fdd, which are about three times larger than fdd for bonds at right angles.