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Organometallics 2010, 29, 354–363 DOI: 10.1021/om900781j
Unveiling the Nature of Binding Interactions of Acetylene and Ethylene with Triangular Coinage Metal Clusters: A DFT Computational Study Athanassios C. Tsipis* Laboratory of Inorganic and General Chemistry, Department of Chemistry, University of Ioannina, 451 10 Ioannina, Greece Received September 8, 2009
Density functional theory calculations have been employed to study the molecular and electronic structures, stabilities, and bonding features of a series of metal clusters with the general formulas [c-M3Ln]þ and [c-M3(μ2-H)3Ln] (M = Cu, Ag, Au; L =ethylene, acetylene; n=1-3) in their singlet ground states. The upright or in-plane orientation adopted by the η2-coordinated unsaturated hydrocarbon ligands L in the [c-M3Ln]þ and [c-M3(μ2-H)3Ln] complexes respectively is strongly related to the electrophilicity index, ω, of the respective electrophilic [c-M3Ln-1]þ and [c-M3(μ2-H)3Ln-1] fragments. We found that for ω > 7 eV the unsaturated ligands adopt the upright orientation, while for ω 7 eV). In contrast, in the hydrido-bridged [c-M3(μ2-H)3Ln] (M=Cu or Ag) clusters involving [c-M3(μ2-H)3Ln-1] fragments of low electrophilicity (ω < 2.95 eV), the unsaturated hydrocarbon ligands exclusively prefer the in-plane conformation. The only exception is the [c-Cu3(μ2-H)3(η2-C2H4)3], 34, cluster, where the orientation of the ethylene ligands deviates slightly (≈5.5) from the perfect in-plane conformation. On the other hand, it should be noticed that in [c-Au3Ln]þ clusters (except [c-Au3(η2-C2H2)]þ, 3, and [c-Au3(η2-C2H4)]þ, 12) the preferred orientation of the unsaturated hydrocarbon ligands deviates from the perfect upright conformation by about 5-45. Nevertheless, in all [c-Au3Ln]þ clusters the unsaturated hydrocarbon ligands L are coordinated with a strongly electrophilic [c-Au3Ln-1]þ fragment (ω> 8 eV). No deviation from the perfect in-plane conformation of the η2-coordinated ligands L was observed in the hydridobridged [c-Au3(μ2-H)3Ln] clusters. In these clusters, the unsaturated hydrocarbon ligands L are, in all cases, coordinated with a [c-Au3(μ2-H)3Ln-1] fragment of low electrophilicity (ω
