LIGAND ADDITIVITY IN THE VALENCE PHOTOELECTRON-SPECTROSCOPY OF PHOSPHINE-SUBSTITUTED MOLYBDENUM CARBONYLS
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The He I valence photoelectron spectra in the 6-9-eV ionization region are reported for the following complexes: Mo-(CO)5PMe3, cis-Mo(CO)4(PMe3)2, trans-Mo(CO)4(PMe3)2, fac-Mo(CO)3(PMe3)3, Mo(CO)5PEt3, trans-Mo(CO)4(PEt3)2, Mo(CO)5P-n-Bu3, and trans-Mo(CO)4(P-n-Bu3)2. The observation of vibrational structure due to excitation of a CO stretching mode in several of the spectra aids band assignment. These data are used to test the validity of the model of ligand additivity for determining the energetics of the d electrons in octahedral d6 complexes. It is shown that the model successfully correlates the positions, intensities, and number of the ionization bands for the above compounds. A comparison of the results for the complexes of different phosphine ligands indicates that PMe3, PEt3, and P-n-Bu3 are comparable -acceptors, but that the -donor strength increases as PMe3 < PEt3 < P-n-Bu3. 1984, American Chemical Society. All rights reserved.