A CASSCF and CCI study of the formation of the Ni2(C2H4) complex

Complete active space SCF and contracted CI calculations have been performed on the potential surface of the Ni₂-C₂H₄ complex in the singlet state. The ethene geometry and position relative to Ni₂ was optimized while the Ni-Ni distance was kept fixed at 2.5 Å.Four possible symmetric geometric arrangements were considered, yielding only an end on -bonded structure as bound. This is a consequence of the charge buildup between the nickel atoms and charge depletion at the ends, coupled with electron mobility along the bond axis, in the nickel dimer.The energy minimum corresponds to a C₂H₄ moiety distorted 21% towards a C₂H₆ geometry, with a bond energy o 24.6 kcal/mol at the CCI level and 28.1 kcal/mol with cluster corrections included. The binding is described by a donation backdonation mechanism. These results are discussed in connection with earlier work on Ni(C₂H₄) and Ni₂(C₂H₄) and in connection with experimental work.