Conformational preferences and electronic structures of bis (.eta.2-ethene)nickel(0) and tris(.eta.2-ethene)nickel(0)

Abstract

Nonempirical molecular electronic structure theory has been applied to the organometallic systems bis(eta/sup 2/-ethene)-nickel(0) and tris(eta/sup 2/-ethene)nickel(0). Three types of contracted Gaussian basis sets have been used in conjunction with restricted self-consistent-field theory. The middle basis set may be labeled Ni(14s 9p 6d/10 s 6p 3d), C (10s 6p/6s 3p), H(5s/3s) and is perhaps the most complete basis set used to date for an experimentally known organotransition metal complex such as Ni(C/sub 2/H/sub 4/)/sub 3/. The chosen basis comes very close to reproducing the exact Hartree-Fock term splittings for the nickel atom. For Ni(C/sub 2/H/sub 4/)/sub 2/ the twisted (D/sub 2d/) and planar (D/sub 2h/) conformations are predicted to lie energetically within 0.1 kcal of each other. For the Ni(C/sub 2/H/sub 4/)/sub 3/ complex, however, the planar conformation lies approx. 24 kcal lower than the upright form. Both of these predictions are in qualitative accord with the earlier semiempirical work of Roesch and Hoffmann. The lowest D/sub 2h/ triplet state of Ni(C/sub 2/H/sub 4/)/sub 2/ is of /sup 3/B/sub 3u/ symmetry, and a number of other electronic states were also investigated. The ionization potentials of both molecules were predicted and large deviations from Koopmans' theorem were found. Mulliken population analysesmore » are also reported and used to qualitatively discuss the electronic structures. 4 figures, 9 tables.« less