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Unveiling the Nature of Binding Interactions of Acetylene and Ethylene with Triangular Coinage Metal Clusters: A DFT Computational Study
(EN)
Tsipis, A. C.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
(EL)
Tsipis, A. C.
(EN)
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-M(3)L(n)](+) and [c-M(3)(mu(2)-H)(3)L(n)] (M = Cu, Ag, Au, L = ethylene, acetylene; n = 1-3) in their singlet ground states. The upright or in-plane orientation adopted by the eta(2)-coordinated unsaturated hydrocarbon ligands L in the [c-M(3)L(n)](+) and [c-M(3)(mu(2)-H)(3)L(n)] complexes respectively is strongly related to the electrophilicity index, omega, of the respective electrophilic [c-M(3)L(n-1)](+) and [c-M(3)(mu(2)-H)(3)-L(n-1)] fragments. We found that for to omega > 7 eV the unsaturated ligands adopt the upright orientation, while for omega < 2.95 eV the in-plane orientation is adopted. The bending back of the H atoms of acetylene and the pyramidalization of the carbon atoms of ethylene upon coordination of ligands L to the metal centers are due to favorable n(M) -> pi*(L) and pi(L) -> n(M) hyperconjugative interactions. Charge (CDA) and energy decomposition analysis (EDA) indicate that acetylene/ethylene are more strongly bound to the "naked" rather than to the hydrido-bridged triangular noble metal clusters, while the M-C(2)H(2)/C(2)H(4) binding interactions are predicted to be predominantly electrostatic rather than covalent. On the basis of the EDA analysis the contribution of pi-back-bonding, and even delta-back-bonding for the acetylene complexes, to the covalent interactions are far more significant than sigma-bonding in [c-M(3)L(n)](+) clusters, while the opposite holds true for the [c-M(3)(mu(2)-H)(3)L(n)] clusters.
(EN)
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