BONDING OF ACETYLENE TO COPPER ATOM, DIMER, AND TRIMER

The bonding of acetylene to copper atom, dimer, and trimer was investigated with a Kohn-Sham density functional approach. Full geometry optimization yielded the equilibrium structures of various Cu(n)C2H2 species. Gradient corrections were included in the calculation of binding energies (BE). The Cu-C2H2 complex was found to have a C(s) structure and a BE of 10 kcal/mol. Three isomers of Cu2C2H2 have similar total energies: a C2nu end-bonded structure with a BE of 18 kcal/mol, and two 1,2-dicupro ethylene isomers-a cis form with a BE of 12 kcal/mol and a trans form with a BE of 15 kcal/mol. Two stable C2nu isomers of Cu3C2H2 were found. In both isomers, the Cu3 ring relaxes from its isosceles structure, with two short bonds (2.247 angstrom) and one long bond (2.478 angstrom), and adopts a nearly equilateral geometry. In one isomer of Cu3C2H2, the acetylene is bonded to one apex of the Cu3 ring with a BE of 29 kcal/mol. In the other, it is bonded to two copper atoms of one side of the Cu3 ring with a BE of 33 kcal/mol. (C) 1994 John Wiley & Sons, Inc.