The gas-phase He I and He II photoelectron spectra of the propynylruthenium molecule CpRu(CO)2CCMe (Cp = η5-C5H5) and the ethynediyldiruthenium molecule [CpRu(CO)2]2(μ-CC) are compared with the spectrum of CpRu(CO)2Cl to experimentally determine electronic structure interactions of the alkynyl ligands with the metal. The spectra indicate that the interaction between the filled metal-dπ and filled alkynyl-π orbitals dominates the metal-alkynyl π electronic structure, mirroring previously characterized CpFe(CO)2 alkynyls. All valence ionizations of the Ru molecules are stabilized with respect to similar Fe compounds, contrary to the common expectation of lower ionization energies with atomic substitution down a column of the periodic table. Ab initio electronic structure calculations suggest that this stabilization traces to the greater inherent electronic relaxation energy associated with removal of Fe 3d electrons compared to removal of Ru 4d electrons. Destabilization of the first two ionization bands of the diruthenium molecule are a result of filled-filled interactions between alkynyl π-bonds with the symmetric combination of metal-metal-dπ orbitals, showing electronic communication between the metals through the alkynyl bridge. From the photoelectron spectrum, this communication was calculated to have a minimum electron-transfer integral of 0.56 eV. The stabilization of the antisymmetric combination of the metal-metal-dπ orbitals gives a direct and unique experimental measure of the interaction with the alkynyl π∗ orbitals. The stabilization caused by the alkynyl π∗ orbitals was found to be approximately one-third of the destabilization caused by the filled-filled interaction with the alkynyl π-bonds and about one-fourth to one-third the stabilization provided by back-bonding to a carbonyl ligand.
|Number of pages||10|
|State||Published - Jan 28 2015|
Bibliographical noteFunding Information:
D.L.L. acknowledges support by the U.S. Department of Energy (Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, DF-SG02-86ER13501 ), the National Science Foundation (Grant No. CHE1111718 ) and the Materials Characterization Program, Department of Chemistry, University of Arizona . J.P.S. acknowledges support by the National Science Foundation (EPSCoR grant EPS-9452895 ). A.R.H. acknowledges the Department of Chemistry and Biochemistry, The University of Arizona for funding of the Molecular Photoelectron Spectroscopy Facility.
© 2014 Elsevier Ltd. All rights reserved.
- Alkynyl ligand
- Metal-metal communication
- Photoelectron spectroscopy
- Robin-Day class
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry