Metal-metal bonding in Rh2(O2CCF3)4: Extensive metal-ligand orbital mixing promoted by filled fluorine orbitals

Dennis L. Lichtenberger, John R. Pollard, Matthew A. Lynn, F. A. Cotton, Xuejun Feng

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20 Scopus citations


He I and He II gas-phase photoelectron spectra of Rh2(O2CCF3)4 are reported. The electron configuration of the metal-metal bond of Rh2(O2CCF3)4 is determined to be σ2 π4 δ2 δ*2 π*4 with an ionization energy order of σ ≃ π > δ > δ* ≃ π*. The δ* and π* ionization energies are similar within the range of vibrational energy separations. Assignment of the Rh-Rh δ ionization is assisted by previous observations that ionizations from δ orbitals in M2(O2CCF3)4 (M = Mo, W) and Mo2(O2CH)4 show enhanced intensity over ionizations from the σ and π orbitals with He II excitation. Changes in ionization energies from the dimolybdenum molecule to the dirhodium molecule and changes in ionization intensities from He I to He II excitation indicate greater metal-ligand mixing in these molecules than observed in other dimetal tetracarboxylates. Amsterdam density functional calculations agree with the observation that the Rh-Rh δ* and π* energies are similar. The calculations also indicate substantial ligand mixing into the metal-metal σ and π orbitals, which is enhanced by the trifluoroacetate ligand despite the inductive withdrawal of electron density by the electronegative fluorine atoms. It is found that a specific set of ligand orbitals that possess the same symmetries as the Rh-Rh σ and π orbitals are destabilized by overlap interactions with the filled fluorine p orbitals, resulting in greater metal - ligand mixing among these orbitals. The increased mixing explains the long-observed enhancement of the δ and δ* ionizations from He I to He II excitation for a number of M2(O2CCF3)4 (M = Mo, W, Ru) systems.

Original languageEnglish (US)
Pages (from-to)3182-3190
Number of pages9
JournalJournal of the American Chemical Society
Issue number13
StatePublished - Apr 5 2000

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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