THE INTERNAL VIBRATIONS OF THE TETRAHETERO-TETRAHEDRANE ANIONS GE-4(4-), SN-4(4-), AND PB-4(4-)

The frequencies of the internal vibrations nu-1 (A1), nu-2(E), nu-3(T2) of the tetrahetero-tetrahedrane anions Ge4(4-) and Sn4(4-) are determined from the infrared and Raman spectra of K7LiGe8 and KSn, respectively. A comparision of the characteristic vibrations of tetrahedrane anions X4(4-) (X = Si, Ge, Sn) and the isoelectronic neutral tetrahedranes Y4 of the neighbouring elements (Y = P, As, Sb) shows a rather constant ratio of the corresponding frequencies kappa = nu(X4(4-))/nu(Y4) = 0,77. This allows for an estimate of nu(Pb4(4-)) from the known Bi4 data. In the infrared spectrum of KPb bands are observed in the predicted frequency range.