A linear combination of Gaussian-type orbital density functional(LCGTO-DF) investigationof three rhenium-oxo complexes, RReO
3 (R =CH
3,
1-C
6H
5,
5-C
5H
5), is presented,showingthe influence of the three different types of ligand-to-metal bonding
![](/images/gifchars/sigma.gif)
-alkyl,
![](/images/gifchars/sigma.gif)
-aryl, and
![](/images/gifchars/pi.gif)
-aryl,respectively. The calculated ionization potentials of thesecompounds are compared to theirHe I photoelectron spectra and found to be in excellent agreement.In particular, the presentresults for H
3C-ReO
3 are much improved overvarious other theoretical approaches. Specialattention is drawn to the -ReO
3 fragment energy levelsand to the nonbonding 2p lone pairson the oxygen atoms; their relative energetic positioning allowsconclusions on the chargedistribution and thus on the Lewis acidity of the rhenium atom in theactive site -ReO
3.To assist this interpretation, Mulliken
fragment charges andcalculated dipole momentsare discussed. A recently proposed relationship between the oxygencharge within the -ReO
3fragment and
17O NMR shifts is supported.