A COMPARATIVE COMPUTATIONAL STUDY OF CATIONIC COINAGE METAL-ETHYLENE COMPLEXES (C2H4)M(+) (M=CU, AG, AND AU)

The cationic (C2H4)M(+) complexes (M = Cu, Ag, and Au) have been exami ned by different ab initio molecular orbital, density functional (DFT) , and density functional/Hartree-Fock (DFT/HF) hybrid methods using re lativistic effective core potentials acid a quasi-relativistic approac h to account for relativistic effects. For (C2H4Au+ a substantial rela tivistic stabilization is observed, such that the computed binding ene rgies are almost twice as high than for (C2H4Ag+ and still significant ly higher than for (C2H4Cu+. Structural features and energetics obtain ed at the various computational levels, although they differ significa ntly in their computational demands, are in satisfying agreement with each other, adding to the level of confidence that can be attributed t o the computationally economic DFT and DFT/HF hybrid methods. In order to determine the nature of the bonding in these (C2H4)M(+) complexes, an energy decomposition scheme is applied to the DFT results. For all three metal cations, the interaction with ethylene shows large covale nt contributions. The major part of the covalent terms stems from sigm a-donor contribution from the ligand to the metal, whereas pi-acceptor bonding (back-bonding) is less important. An atoms-in-molecules (ATM) analysis of the charge density distribution reveals cyclic structures for (C2H4Au+ and (C2H4Cu+, whereas (C2H4Ag+ is T-shaped.