as indicated above,4 we are in the presence of d13, dI4, and dI5 species, respectively, but metal-oxygen triple bonding cannot be obviously proposed, for the closed-shell configuration of the metals is far from being obtained and involvement of oxygen d orbitals in bonding seems quite unrealistic. The magnetic and structural features in compounds of this type with the metals in octahedral environments have been often rationalized through qualitative MO pictures similar to that of Figure 2b.I4 Notice that the HOMO eg level is nonbonding and that the removal of two or four electrons from it (corresponding to dI4 or dI3 initial electron counts) does not alter the overall M U M bonding network.Acknowledgment. We are deeply indebted to Professor Roald Hoffmann for hosting and guiding C.M. at Cornel1 University. We are grateful to Dr. T. A. Albright for some comments. Thanks are also due to Mr. Franco Cecconi for drawings.
AppendixAll calculations were performed with use of the extended Huckel methods.15 The programs, kindly supplied by Proffessor Roald Hoffmann, were implemented and run on an SEL 32/70 computer. The parameters used for Co, Ni, and Cr were taken from ref 5b. P-H, N-H, and C-O distances were idealized at 1.40, 1.09, and 1.15 A, respectively. The M-S, M-P, and M-C bond lengths were taken from the experimental values of related structures.We have recently been investigating the vibrational spectroscopy of metal cluster systems, particularly of osmium carbonyl derivatives. It has been suggested that some clusters may be catalytically important and that they may provide model compounds for the study of chemisorbed species on metal surfaces.'-3 For this reason a detailed understanding of the vibrational spectra of such compounds should aid the interpretation of the spectra of chemisorbed species. Examples of the use of the infrared spectra of metal cluster compounds in interpreting the vibrational spectra obtained from metal ( I ) Robinson, A. L. Science (Washington, D.C.) 1976 194, 1150. (2) (a) Muetterties, E. L. Bull. SOC. Chim. Eelg. 1975, 84, 959. (b) Muetterties, E. L.; Thasin, T. N.; Band, Elliot; Brucker, C. F.; Pretzer, W. R. Chem. Rev. 1979, 79, 91. (3) Privet, M.; Bassett, J. M.; Labowski, E.; Mattieu, M. V. J . Am. Chem. SOC. 1975, 97, 3655. (4) Jayasooriya, U. A.; Chesters, M. A.; Howard, M. W.; Kettle, S. F. A,; Powell, D. B.; Sheppard, N. Surf Sci. 1980, 93, 526. b H / Figure 1. Structures of (a) HOs,(CH=CH,)(CO),, and (b) H2-OsS(C=CH,)(C0)9. surface species are contained in a number of recent publications (see, for example, ref 4).In this paper we report the vibrational spectra and assignments of two metal cluster compounds, incorporating unusual olefinic groups, of formulas H O S~( C H = C H~) ( C O ) ,~ and H20s3(C=CH2)(C0)~~6 with the structures shown in Figure la,b. The spectra and the interpretation described here confirm previous suggestions, based on X-ray crystallographic data,6 that in these compounds the olefinic groups are both u and 7r bonded. In metal surface studies of chemisor...