| Ultraviolet photoelectron (PE) spectroscopy and molecular orbital (MO) calculations were performed on ((mu)(,3)-CR)Co(,3)(CO)(,9) (R = Cl,Br,I,H,Me,OMe), SCo(,3)(CO)(,9), SH(,n-1)Fe(,n)Co(,3-n)(CO)(,9) (n = 1,2,3), S(,2)Fe(,3)(CO)(,9), SH(,2)M(,3)(CO)(,9) (M = Fe,Ru,Os), ((mu)-H)((mu)-X)Os(,3)(CO)(,10) and ((mu)-X)(,2)Os(,3)(CO)(,10) (X = Cl,Br,I). For the ((mu)(,3)-CR)Co(,3)(CO)(,9) (R = Cl,Br,I,H,Me,OMe) the lowest ionization energy corresponds to a delocalized orbital which is both Co-C and Co-Co bonding. This ionization band is closely followed by bands due to Co-Co and Co-CO (pi) interactions. Comparison of the PE spectra of H(,3)CX, HC(TBOND)CX, C(,6)H(,5)X, and ((mu)(,3)-CR)Co(,3)(CO)(,9) for the halogens suggests that the (pi) bonding of the cobalt cluster to the apical C is closer to HC(TBOND)CX or C(,6)H(,5)X than it is to H(,3)CX. The localized MO description for these clusters can be best described with an sp-hybridized apical C, in which the lone pair forms a dative bond to the basal metal triangle and the remaining p orbitals form multicentered bonds to the Co(,3) system. In the SH(,n-1)Fe(,n)Co(,3-n)(CO)(,9) (n = 1, 2, 3) series as the Co atoms are replaced by the isoelectronic FeH unit, the PE spectra show the loss of a Co band and the appearance of an Fe band. This phenomenon suggests that the 3d bands may localize upon ionization. In a comparison with the PE spectrum of M(,3)(CO)(,12) (M = Fe,Ru,Os), the major spectral changes for SH(,2)M(,3)(CO)(,9) (M = Fe,Ru,Os) are the loss of a band corresponding to direct M-M interactions and the appearance of bands due to a mixture of energy equivalent M-H-M and M-S interactions. The PE spectra also show a substantial rearrangement of M t(,2g)-like bands, which are usually considered M-CO (pi) bonding. It is the filled, antibonding M-S interaction with the t(,2g)-like orbitals, which corresponds to the band in the PE spectra between the M-M and the t(,2g)-like band. In the comparison with the PE spectrum of Os(,3)(CO)(,12), the major spectral changes for ((mu)-H)((mu)-X)Os(,3)(CO)(,10) and ((mu)-X)(,2)Os(,3)(CO)(,10) (X = Cl,Br,I) are the loss of intensity in the ionization band corresponding to direct Os-Os interactions and the appearance of bands due to M-X and/or M-H-M interactions. Shifts in the bands corresponding to the Os t(,2g)-like orbitals are observed. The MO calculations suggest that the t(,2g)-like Os(CO)(,3) orbitals interact with the bridging H and halogen atoms to produce these observed shifts. The MO calculations suggest that the only direct Os-Os bond in both series are the two (CO)(,4)Os-Os(CO)(,3) bonds and that the (CO)(,3)Os-Os(CO)(,3) interaction in the (HX) series is weakly bonding, while that in (X)(,2) series is weakly antibonding. |
