The valence electronic structure of several compounds containing triple bonds between molybdenum atoms has been investigated by using molecular orbital theory and photoelectron spectroscopy (PES). Xα-SW calculations have been performed on Mo2(OH)6, Mo2(NH2)6, Mo2(NMe2)6, and Mo2(CH3)6, and the projected Xa formalism has been used to determine accurate orbital populations and atomic charges. The calculated transition state ionization potentials agree quite favorably with the He I PE spectra of Mo2(OCH2CMe3)6, Mo2(NMe2)6, and Mo2(CH2SiMe3)6. The 7-10-eV binding energy region of Mo2- (OCH2CMe3)6 shows three well-resolved bands which are assigned to Mo-Mo bond, Mo-Mo bond, and O lone-pair ionizations, in order of increasing ionization potential. The spectra of the dimethylamido and trimethylsilylmethyl derivatives are more complicated due to the interspersing of metal- and ligand-based ionizations, but they are quite satisfactorily assigned by the calculations. Atomic charge analysis indicates significantly greater ligand-to-metal donation in Mo2(CH3)6 than in the alkoxy or amido derivatives. This has been used to explain trends in the structure and reactivity of the compounds. Finally, the calculations are used to dispute the recent proposal that the eclipsed rotational confomer should be preferable to the staggered conformer for small ligands. © 1980, American Chemical Society. All rights reserved.
