Experimental and theoretical study of monoligand complexes of nickel atoms with simple alkynes

Abstract

Monoligand complexes of nickel atoms with simple alkynes have been investigated by kinetic studies of association reactions of nickel atoms with ethyne, propyne, and 2-butyne in the gas phase near room temperature, and by quantum chemical calculations on the Ni[C2H2] complex using a Linear Combination of Gaussian-Type Orbitals – Density Functional (LCGTO–DF) method. Experimental estimates of binding energies of the monoligand complexes have been made by using RRKM unimolecular reaction theory to model the pressure dependence of second-order rate coefficients for the association reactions: [Formula: see text] and 29 ± 5 kcal mol−1, for Ni[C2H2], Ni[propyne], and Ni[2-butyne], respectively. The trend in binding energy with methyl substitution on ethyne is discussed and compared with similar data for monoligand complexes of alkynes with copper atoms. The harmonic vibrational frequencies and binding energy for the 1A1 ground state of Ni[C2H2] have been calculated using the LCGTO–DF method, and the results are compared with experimental data on the infrared spectrum of matrix-isolated Ni[C2H2] and with the estimate of the binding energy of Ni[C2H2] from the present experimental study. There is excellent agreement between the experimental and theoretical results. The calculations indicate that at least one triplet state of Ni[C2H2] is bound relative to ground state Ni + C2H2 reactants. This is consistent with indications from the kinetic results that the association reaction occurs on more than one potential energy surface.