VIBRATIONAL SPECTRA AND BONDING IN ISOSTRUCTURAL $X_{3}MM' (CO)_{4}$ METAL-METAL BONDED SYSTEMS

Author Institution: Department of Chemistry, Brown UniversityThe infrared and laser Raman spectra of the ions $Cl_{3}GeFe (CO)_{4}^{-}, Cl_{3}SnFe(CO)_{4}^{-},$ and $Br_{3}SnFe (CO)_{4}^{-}$ are reported, and 15 to 18 of the 20 observable fundamentals for each ion have been observed and assigned on the basis of $C_{3v}$ symmetry. Vibrational analyses of these spectra and those of the isostructural $X_{3}MCo(CO)_{4}$ 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 $MX_{3}$ 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