TY - JOUR
T1 - Comparison of the Bonding of Benzene and C60 to a Metal Cluster
T2 - Ru3(CO)9(μ3-η2,η 2,η2-C6H6) and Ru3(CO)9(μ3-η2,η 2,η2-C60)
AU - Lynn, Matthew A.
AU - Lichtenberger, Dennis L.
N1 - Funding Information:
MAL thanks the National Science Foundation for a predoctoral fellowship. DLL acknowledges support by the U.S. Department of Energy (Division of Chemical Sciences, Office of Basic Energy Science, Office of Energy Research, DE-FG03-95ER14574) for small molecule interactions with metals, the National Science Foundation (Grant No. CHE9405134) for contributions to the equipment, and the Materials Characterization Program, Department of Chemistry, University of Arizona. MAL and DLL thank Professor John Shapley and Hsiu-Fu Hsu for providing crystallographic data for Ru3(CO)9(+3-’2,’2,’2-C60).
PY - 2000
Y1 - 2000
N2 - The electron distributions and bonding in Ru3(CO)9(μ3-η2,η 2,η2-C6H6) and Ru3(CO)9(μ3-η2,η 2,η2-C60) are examined via electronic structure calculations in order to compare the nature of ligation of benzene and buckminsterfullerene to the common Ru3(CO)9 inorganic cluster. A fragment orbital approach, which is aided by the relatively high symmetry that these molecules possess, reveals important features of the electronic structures of these two systems. Reported crystal structures show that both benzene and C60 are geometrically distorted when bound to the metal cluster fragment, and our ab initio calculations indicate that the energies of these distortions are similar. The experimental Ru-Cfullerene bond lengths are shorter than the corresponding Ru-Cbenzene distances and the Ru-Ru bond lengths are longer in the fullerene-bound cluster than for the benzene-ligated cluster. Also, the carbonyl stretching frequencies are slightly higher for Ru3(CO)9(μ3-η2,η 2,η2-C60) than for Ru3(CO)9(μ3-η2,η 2,η2-C6H6). As a whole, these observations suggest that electron density is being pulled away from the metal centers and CO ligands to form stronger Ru-Cfullerene than Ru-Cbenzene bonds. Fenske-Hall molecular orbital calculations show that an important interaction is donation of electron density in the metal-metal bonds to empty orbitals of C60 and C6H6. Bonds to the metal cluster that result from this interaction are the second highest occupied orbitals of both systems. A larger amount of density is donated to C60 than to C6H6, thus accounting for the longer metal-metal bonds in the fullerene-bound cluster. The principal metal-arene bonding modes are the same in both systems, but the more band-like electronic structure of the fullerene (i.e., the greater number density of donor and acceptor orbitals in a given energy region) as compared to C6H6 permits a greater degree of electron flow and stronger bonding between the Ru3(CO)9 and C60 fragments. Of significance to the reduction chemistry of M3(CO)9(μ3-η2,η 2,η2-C60) molecules, the HOMO is largely localized on the metal-carbonyl fragment and the LUMO is largely localized on the C60 portion of the molecule. The localized C60 character of the LUMO is consistent with the similarity of the first two reductions of this class of molecules to the first two reductions of free C60. The set of orbitals above the LUMO shows partial delocalization (in an antibonding sense) to the metal fragment, thus accounting for the relative ease of the third reduction of this class of molecules compared to the third reduction of free C60.
AB - The electron distributions and bonding in Ru3(CO)9(μ3-η2,η 2,η2-C6H6) and Ru3(CO)9(μ3-η2,η 2,η2-C60) are examined via electronic structure calculations in order to compare the nature of ligation of benzene and buckminsterfullerene to the common Ru3(CO)9 inorganic cluster. A fragment orbital approach, which is aided by the relatively high symmetry that these molecules possess, reveals important features of the electronic structures of these two systems. Reported crystal structures show that both benzene and C60 are geometrically distorted when bound to the metal cluster fragment, and our ab initio calculations indicate that the energies of these distortions are similar. The experimental Ru-Cfullerene bond lengths are shorter than the corresponding Ru-Cbenzene distances and the Ru-Ru bond lengths are longer in the fullerene-bound cluster than for the benzene-ligated cluster. Also, the carbonyl stretching frequencies are slightly higher for Ru3(CO)9(μ3-η2,η 2,η2-C60) than for Ru3(CO)9(μ3-η2,η 2,η2-C6H6). As a whole, these observations suggest that electron density is being pulled away from the metal centers and CO ligands to form stronger Ru-Cfullerene than Ru-Cbenzene bonds. Fenske-Hall molecular orbital calculations show that an important interaction is donation of electron density in the metal-metal bonds to empty orbitals of C60 and C6H6. Bonds to the metal cluster that result from this interaction are the second highest occupied orbitals of both systems. A larger amount of density is donated to C60 than to C6H6, thus accounting for the longer metal-metal bonds in the fullerene-bound cluster. The principal metal-arene bonding modes are the same in both systems, but the more band-like electronic structure of the fullerene (i.e., the greater number density of donor and acceptor orbitals in a given energy region) as compared to C6H6 permits a greater degree of electron flow and stronger bonding between the Ru3(CO)9 and C60 fragments. Of significance to the reduction chemistry of M3(CO)9(μ3-η2,η 2,η2-C60) molecules, the HOMO is largely localized on the metal-carbonyl fragment and the LUMO is largely localized on the C60 portion of the molecule. The localized C60 character of the LUMO is consistent with the similarity of the first two reductions of this class of molecules to the first two reductions of free C60. The set of orbitals above the LUMO shows partial delocalization (in an antibonding sense) to the metal fragment, thus accounting for the relative ease of the third reduction of this class of molecules compared to the third reduction of free C60.
KW - Electronic structure
KW - Fullerene
KW - Metal cluster
KW - Molecular orbital
KW - Ruthenium
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U2 - 10.1023/A:1009021000300
DO - 10.1023/A:1009021000300
M3 - Article
AN - SCOPUS:0034404671
SN - 1040-7278
VL - 11
SP - 169
EP - 188
JO - Journal of Cluster Science
JF - Journal of Cluster Science
IS - 1
ER -