Vibrational spectra of the cluster anions. 1 vibrational spectra of the cluster anions [E-4](4-) and barium compounds Na4E4 and Ba2E4 (E = Si, Ge)

Abstract

The vibrational spectra of the cluster anions [E-4](4-)(E = Si, Ge) in the metallic compounds Ba2E4 and Na4E4 have been measured and assigned based on the T-d symmetry of the discrete tetrahedranide anion. Due to the lower site-symmetries in the respective crystals all degenerate modes are split, but to different extends. The characteristic breathing frequency nu (E-E) of the [E-4](4-) cluster appears exclusively in the Raman spectrum and is almost unaffected by the nature of counterions: nu (E-E) = 486 cm(-1) (E = Si) and 276 and 278 (Ge), respectively. The calculated valence force constants f(d) (Si-Si)= 1.17 Ncm(-1) (Na); 1.15 Ncm(-1) (Ba) and f(d) (Ge-Ge) = 0.98 Ncm(-1) (Na); 0.94 Ncm(-1) (Ba) are in good agreement with those previously reported.