Knowledge Bank

The infrared and laser Raman spectra of the ions $Cl3GeFe(CO)4-,Cl3SnFe(CO)4-,$ and $Br3SnFe(CO)4-$ are reported, and 15 to 18 of the 20 observable fundamentals for each ion have been observed and assigned on the basis of $C3v$ symmetry. Vibrational analyses of these spectra and those of the isostructural $X3MCo(CO)4$ molecules (M = Ge, Sn; X = Cl, Br, I) have been carried out with a uniform set of approximations, which lead to close ``calculated-observed” agreement while both holding the force fields for the $M\prime (CO)4$ moiety constant through the respective series and varying only the constants associated with the $MX3$ moieties. In each of the three isoelectronic pairs between the two series, k(Fe-M) is in a range higher than that for the analogous k(Co-M). The range of approximations over which this result remains valid, and the nature of bonding implications which can be drawn from vibrational analysis of such organometallic compounds, are evaluated.